Apparatus and method for testing defects

ABSTRACT

A defect inspection method includes radiating an illumination slit-shaped beam having lights substantially parallel to a longitudinal direction to a substrate having circuit patterns in a direction inclined at a predetermined gradient relative to the direction of a line normal to the substrate and inclined at a predetermined gradient on a surface with respect to a group of main straight lines of the circuit patterns with its longitudinal direction oriented almost perpendicularly to a direction of a movement of the substrate. Scattered light reflected by a defect such as a foreign particle existing on the illuminated substrate is received and converted into a detection signal by using an image sensor, and defect judging is effected of an extracted a signal indicating a defect such as a foreign particle on the basis of the detection signal output.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.09/362,135, filed Jul. 28, 1999 which is a continuation-in-part of U.S.application Ser. No. 08/535,577, filed Sep. 28, 1995, which is acontinuation application of U.S. application Ser. No. 08/046,720, filedApr. 16, 1993, now U.S. Pat. No. 5,463,459, which is acontinuation-in-part of U.S. application Ser. No. 07/679,313, filed Apr.2, 1991, now U.S. Pat. No. 5,233,191 and U.S. application Ser. No.07/778,363, filed Oct. 17, 1991, now U.S. Pat. No. 5,274,434.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a defect testing apparatus and adefect testing method for inspecting a state of generation of defectssuch as foreign particles in a fabrication process such as asemiconductor fabrication process, a liquid-crystal-display fabricationprocess and a print-board fabrication process wherein a defect such as aforeign particle generated in a process to create a pattern on asubstrate to produce an object is detected and analyzed in order todetermine a countermeasure.

[0003] In the conventional semiconductor fabrication method, a foreignparticle existing on a semiconductor substrate also known as a wafercauses a defect such as poor insulation of a wire or a short circuit.Furthermore, in the case of a miniaturized semiconductor device, aninfinitesimal foreign particle existing in a semiconductor substrateresults in poor insulation of a capacitor or destruction of typically agate oxide film. These foreign particles are introduced to get mixedwith a semiconductor material in a variety of states due to a variety ofcauses For example, a foreign particle is generated by a movable part ofa transportation apparatus or a human body A foreign particle can alsobe generated as a result of a chemical reaction in processing equipmentusing a process gas or mixed with chemicals or a raw material.

[0004] Likewise, if a foreign particle is introduced to get mixed with apattern, causing some defects in a process to fabricate a liquid-crystaldisplay device, the resulting display device is not usable. The processto fabricate a print board is in the same situation, That is to say, amixed foreign particle causes a poor connection and a short circuit in apattern.

[0005] One of publications for detecting a foreign particle on asemiconductor substrate of this type is disclosed in Japanese PatentLaid-open No. Sho 62-89336 and referred to hereafter as publication 1.According to this prior art, a laser beam is radiated to a semiconductorsubstrate. If a foreign particle is stuck to the semiconductorsubstrate, the foreign particle will generate scattered beams which canthen be detected and compared with a result of inspection for asemiconductor substrate of the same type inspected immediately before.In this way, a difference in inspection result can be detected and usedto eliminate a pattern defect. As a result, a foreign particle and adefect can be detected with a high degree of sensitivity and a highdegree of reliability. Another publication referred to hereafter aspublication 2 is disclosed in Japanese Patent Laid-open No. Sho63-135848. According to this publication, a laser beam is radiated to asemiconductor substrate. If a foreign particle is stuck to thesemiconductor substrate, the foreign particle will generate scatteredbeams which can then be detected. A detected beam generated by a foreignparticle is analyzed by using an analysis technique such as laser photoluminescence or a secondary X-ray analysis (XMR).

[0006] In addition, as a technology for detecting a foreign particle,there is also known a technique whereby a coherent beam is radiated to awafer, and the beam reflected by repetitive patterns on the wafer isremoved by˜ a spatial filter to emphasize light components generated bya foreign particle or a defect which does not exhibit repetitiveness. Inthis way,’ a foreign particle or a defect can be detected.

[0007] A technology disclosed in Japanese Patent Laid-open No. Hei1-117024 is referred to hereafter as publication 3. According to thispublication, in a foreign particle inspecting apparatus, a beam isradiated to a circuit pattern on a wafer in a direction forming an angleof 45 degrees with respect to a group of main straight lines of thecircuit pattern and a 0th-order diffracted beam from the group of mainstraight lines is introduced into the aperture of an objective lens. Thedisclosure also includes a description which states that, according topublication 3, a beam from any group of straight lines other than thegroup of main straight lines is shielded by a spatial filter.

[0008] In addition, other publications related to apparatuses andmethods for detecting defects such as foreign particles are disclosed inJapanese Patent Laid-open No. Hei 1-250847, Japanese Patent Laid-openNo. Hei 6-258239, Japanese Patent Laid-open No. Hei 6-324003, JapanesePatent Laid-open No. Hei 8-210989 and Japanese Patent Laid-open No. Hei8-271437 and referred to as publications 4, 5, 6 ,7 and 8 respectively.With publications 1 to 8 mentioned above, however, it is impossible todetect a defect such as an infinitesimal foreign particle on asubstrate, on which repetitive patterns coexist with non-repetitivepatterns, at a high speed, with ease and with a high degree ofsensitivity.

[0009] To put it in detail, publications 1 to 8 have a problem of asubstantially reduced sensitivity (increased minimum dimensions of adetected foreign particle) in the case of a part of the substrate otherthan the repetitive portion such as memory cells.

[0010] In addition, publications 1 to 8 also have a problem of asubstantially reduced sensitivity in the case of an oxide film whichpasses a radiation beam.

[0011] Moreover, publications 1 to 8 also have a problem of inability todetect a defect such as an infinitesimal foreign particle.

[0012] Furthermore, in the case of publications 1 to 8, amass-production build-up line or a pilot line and a mass-production lineof a semiconductor production process are not distinguished from eachother. That is to say, inspection equipment used in the mass-productionbuild-up work is also used in a mass-production line without change inspite of the fact that it is necessary to early detect generation of aforeign particle on the mass-production line and determine acountermeasure for the detected foreign particle.

[0013] At any rate, the conventional defect inspecting apparatus islarge in size and has such a configuration that the apparatus must beinstalled independently. For this reason, in order to inspect a foreignparticle and a defect, it is necessary to transport a semiconductorsubstrate, a liquid-crystal-display substrate or a print substrate whichhas been processed along the mass-production line to a place at whichthe defect inspecting apparatus is installed. That is to say, it takestime to transport the substrate and to inspect the substrate for aforeign particle and a defect. As a result, complete inspection isdifficult. In addition, it is hard to carry out such sampling inspectionat a sufficiently high frequency.

[0014] Further, a defect inspecting apparatus with such a configurationrequires an operator.

SUMMARY OF THE INVENTION

[0015] It is thus an object of the present invention addressing theproblems described above to provide a defect inspecting apparatus and adefect inspection method capable of inspecting a defect such as aninfinitesimal foreign particle on an inspected substrate containingrepetitive patterns, non-repetitive patterns and non-patterns whichcoexist with each other at a high speed and with a high degree ofprecision.

[0016] It is another object of the present invention to provide a defectinspecting apparatus and a defect inspection method which allow ahigh-efficiency substrate fabrication line to be constructed byimplementation of complete inspection and sampling inspection at asufficiently high frequency.

[0017] It is still another object of the present invention to provide adefect inspecting apparatus and a defect inspection method which arecapable of inspecting also a defect such as an extremely infinitesimalforeign particle having a size of the order of 0.1 μm or smaller at ahigh speed and with a high degree of sensitivity by effectivelyutilizing the light quantity of a Gaussian beam generated by an ordinaryinexpensive light source such as a laser-beam source.

[0018] It is a further object of the present invention to provide adefect inspecting apparatus and a defect inspection method which arecapable of inspecting also a defect such as an extremely infinitesimalforeign particle having a size of the order of 0.1 μm or smaller at ahigh speed and with a high degree of sensitivity by effectivelyutilizing the light quantity of a Gaussian beam generated by typically alaser-beam source and by resolving a problem of a lack of illuminationat regions surrounding an area on a substrate being inspected due to adecrease in MTF at locations separated away from an optical axis in adetection optical system.

[0019] It is a still further object of the present invention to providea defect inspecting apparatus capable of inspecting a defect such as areal foreign particle by setting the level of a threshold value at aproper degree of sensitivity without substantially increasing the amountof generated false information wherein the threshold value is used as acriterion as to whether or not a defect exists in a variety ofcircuit-pattern areas in the device structure laid out on a substratebeing inspected.

[0020] It is a still further object of the present invention to providea defect inspecting apparatus capable of inspecting a defect such as aforeign particle with a specified size to be detected by setting thelevel of a threshold value used as a criterion as to whether or not adefect exists for the size of the defect to be detected in a variety ofcircuit-pattern areas in the device structure laid out on a substratebeing inspected.

[0021] It is a still further object of the present invention to providea defect inspecting apparatus capable of inspecting a defect such as aforeign particle by allowing the size of the defect existing in avariety of circuit-pattern areas in the device structure laid out on asubstrate being inspected to be inferred.

[0022] It is a still further object of the present invention to providea semiconductor-substrate fabricating method for fabricating asemiconductor substrate at a high efficiency and, hence, at a highyield.

[0023] In order to achieve the objects described above, the presentinvention provides a defect inspecting apparatus and a defect inspectionmethod adopted by the defect inspecting apparatus comprising: a stagefor mounting and moving an inspected substrate with a circuit patterncreated thereon; an illumination optical system for illuminating thesubstrate by forming a beam radiated by a light source into aslit-shaped beam and directing the beam toward the substrate beinginspected at a predetermined gradient of (π/2−α1) with respect to thedirection of a line normal to the substrate and a predetermined gradientof Φ1 with respect to a group of main straight lines of the circuitpattern on the surface of the substrate wherein the longitudinaldirection is almost perpendicular to a direction of the y axis of themovement of the stage; a detection optical system including an imagesensor for receiving scattered beams reflected by a defect such as aforeign particle existing on the inspected substrate illuminated by theslit-shaped beam radiated by the illumination optical system and forconverting the scattered beams into a detection signal representing aresult of detection of the defect; and an image-signal processing unitfor extracting a signal showing the defect such as a foreign particle onthe basis of the detection signal output by the image sensor employed inthe detection optical system.

[0024] In addition, in order to achieve the objects described above, thepresent invention also provides a defect inspecting apparatus and adefect inspection method adopted by the defect inspecting apparatuscomprising: a stage for mounting and moving an inspected substrate withcircuit patterns created thereon; an illumination optical system forilluminating the substrate by forming a beam radiated by a light sourceinto a slit-shaped beam and directing the beam toward the substratebeing inspected at a predetermined gradient of (π/2−α1) with respect tothe direction of a line normal to the substrate and a predeterminedgradient of Φ1 with respect to a group of main straight lines of thecircuit pattern on the surface of the substrate wherein the longitudinaldirection is almost perpendicular to a direction of the y axis of themovement of the stage; a detection optical system including an imagesensor for receiving scattered beams reflected by a defect such as aforeign particle existing on the inspected substrate illuminated by theslit-shaped beam radiated by the illumination optical system and forconverting the scattered beams into a detection signal representing aresult of detection of the defect; and an image processing unit having:a criterion setting means which calculates a variation of the detectionsignal output by the image sensor of the detection optical system torepresent a variation of a scattered beam reflected by areas on thesurface of the substrate in which the naturally identical circuitpatterns are created or regions in close proximity to the areas andwhich sets a criterion (threshold value) based on the calculatedvariation; and a signal extracting means which extracts a signal showingthe defect such as a foreign particle from the detection signal outputby the image sensor employed in the detection optical system on thebasis of the criterion set by the criterion setting means.

[0025] Furthermore, the present invention also provides a defectinspecting apparatus and a defect inspection method adopted by thedefect inspecting apparatus comprising: a stage unit for mounting andmoving an inspected substrate with a circuit pattern created thereon; anillumination optical system for illuminating the substrate by forming abeam radiated by a light source into a slit-shaped beam and directingthe beam toward the substrate being inspected at a predeterminedgradient with respect to the direction of a line normal to the substrateand a predetermined gradient with respect to a group of main straightlines of the circuit pattern on the surface of the substrate wherein thelongitudinal direction is almost perpendicular to a y direction of themovement of the stage; a detection optical system including an imagesensor for receiving scattered beams reflected by a defect such as aforeign particle existing on the inspected substrate illuminated by theslit-shaped beam radiated by the illumination optical system and forconverting the scattered beams into a detection signal representing aresult of detection of the defect; and an image-signal processing unitfor extracting a signal showing the defect such as a foreign particlefrom the detection signal output by the image sensor employed in thedetection optical system on the basis of a criterion (threshold value)set for each of a variety of areas composing the circuit pattern.

[0026] Moreover, in the defect inspecting apparatuses and the defectinspection methods provided by the present invention, the predeterminedgradient of Φ1 of the slit-shaped beams with respect to a group of mainstraight lines of the circuit pattern on the surface of the substrate isabout 45 degrees.

[0027] Further, in the defect inspecting apparatuses and the defectinspection methods provided by the present invention, the optical axisof the detection optical system is substantially perpendicular to thesubstrate being inspected.

[0028] In addition, in the defect inspecting apparatuses and the defectinspection methods provided by the present invention, the optical axisof the detection optical system is inclined with respect to the linenormal to the substrate being inspected.

[0029] Furthermore, in the defect inspecting apparatus provided by thepresent invention, the light source employed in the illumination opticalsystem is a laser-beam source.

[0030] Moreover, in the defect inspecting apparatus provided by thepresent invention, the illumination optical system has an opticalelement of a shape resembling a cone for generating a converged light.

[0031] Further, in the defect inspecting apparatus provided by thepresent invention, the illumination optical system is provided with anoptical system for radiating a white light in a direction inclined withrespect to a normal line to a substrate being inspected.

[0032] In addition, in the defect inspecting apparatus provided by thepresent invention, the illumination optical system is provided with aspace filter.

[0033] Furthermore, in the defect inspecting apparatus provided by thepresent invention, the image sensor employed in the detection opticalsystem is a TDI (Time Delay Integration) image sensor.

[0034] Moreover, the present invention provides a defect inspectingapparatus comprising: an illumination optical system having an opticalelement of a shape resembling a cone for radiating an illumination lightbeam in a direction at a predetermined gradient with respect to a linenormal to the surface of an object of inspection and for converging theillumination light beam in at least one direction on the surface of theobject of inspection; a detection optical system including an imagesensor which receives a light reflected by the object of inspection andconverts the received light into a detection signal; and an image-signalprocessing unit for processing the detection signal output by thedetection optical system.

[0035] Further, the detection optical system employed in the defectinspecting apparatus provided by the present invention has: a beamsplitting optical system for splitting a light beam reflected by theobject of inspection into reflected beams with one of the reflectedbeams having an intensity of about {fraction (1/100)} of that ofanother; and a plurality of image sensors for receiving each of thereflected beams split by the beam splitting optical system.

[0036] In addition, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection on which aplurality of circuit patterns with substantially identical shapes arelaid out; a detection optical system including an image sensor forreceiving a light reflected by the object of inspection and forconverting the received light into a detected image signal; and animage-signal processing unit for processing the detected image signaland being provided with: a criterion setting means which calculates avariation of an image signal among pixels which correspond to thecircuit patterns with identical shapes or pixels in close proximitythereto on the basis of the image signal detected by the detectionoptical system and which sets a threshold value to serve as a criterionas to whether or not a defect such as a foreign particle exists on thebasis of the calculated variation of the image signal; and a judgmentmeans which forms a judgment as to whether or not a defect exists fromthe image signal detected by the detection optical system on the basisof the criterion set by the criterion setting means.

[0037] Furthermore, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection on which aplurality of patterns with substantially identical shapes are laid out;a detection optical system including an image sensor for receiving alight reflected by the object of inspection and for converting thereceived light into a detected image signal; and an image-signalprocessing unit for processing the detected image signal and beingprovided with: a difference computing means which computes differencesin image signal among pixels corresponding to the patterns havingidentical shapes on the basis of an image signal detected by thedetection optical system; a criterion setting means which calculates avariation of the differences computed by the difference computing meansat a plurality of for pixels adjacent to pixels used for forming ajudgment as to whether or not a defect such as a foreign particle existsand which sets a criterion of the level of a pixel signal used fordetermining whether or not the defect such as the foreign particleexists on the basis of the calculated variation; and a judgment meanswhich forms a judgment as to whether or not the defect exists from theimage signal detected by the detection optical system on the basis ofthe criterion set by the criterion setting means.

[0038] Moreover, in the defect inspecting apparatus provided by thepresent invention, the image-signal processing unit has an output meanswhich outputs pieces of a result of defect inspection produced by thejudgment means and data representing the criterion set by the criterionsetting means.

[0039] Further, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection on which aplurality of patterns with substantially identical shapes are laid out;a detection optical system including an image sensor for receiving alight reflected by the object of inspection and for converting thereceived light into a detected image signal; and an image-signalprocessing unit having: a judgment means which forms a judgment as towhether or not a defect exists by comparison of the image signal outputby the detection optical system with a criterion; and a display meanswhich displays map information or images on the patterns havingidentical shapes to be used as the criterion by the judgment means, orwhich displays relations between criteria (or sensitivities) andindicators of inspection area for them, or which displays sensitivityinformation on circuit patterns having identical shapes corresponding tocriteria.

[0040] In addition, the image-signal processing unit employed in thedefect inspecting apparatus provided by the present invention has anarea priority mode, a standard mode and a sensitivity priority mode ascondition specifying modes.

[0041] Furthermore, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection on which aplurality of patterns with substantially identical shapes are laid out;a detection optical system including an image sensor for receiving alight reflected by the object of inspection and for converting thereceived light into a detected image signal; and an image-signalprocessing unit for processing the detected image signal and beingprovided with: a criterion setting means which sets a criterion byvarying the criterion in accordance with a state of an underlying layerin the patterns with identical shapes; and a judgment means which formsa judgment as to whether or not a defect exists by comparison of theimage signal output by the detection optical system with the criterionset by the criterion setting means.

[0042] Moreover, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection on which aplurality of patterns with substantially identical shapes are laid out;a detection optical system including an image sensor for receiving alight reflected by the object of inspection and for converting thereceived light into a detected image signal; and an image-signalprocessing unit for processing the detected image signal output by thedetection optical system and being provided with: a size specifyingmeans which specifies a size of a defect; a criterion setting meanswhich sets a criterion by varying the criterion in accordance with thedefect size specified by the size specifying means; and a judgment meanswhich forms a judgment as to whether or not a defect exists bycomparison of the image signal output by the detection optical systemwith the criterion set by the criterion setting means.

[0043] Further, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection on which aplurality of patterns with substantially identical shapes are laid out;a detection optical system including an image sensor for receiving alight reflected by the object of inspection and for converting thereceived light into a detected image signal; and an image-signalprocessing unit for processing the detected image signal output by thedetection optical system and being provided with: a size specifyingmeans which specifies a size of a defect; and a control means whichcontrols the power of the illumination light radiated by theillumination optical system in accordance with the defect size specifiedby the size specifying means.

[0044] In addition, the present invention provides a defect inspectingapparatus comprising: an image-pickup optical system having: anillumination optical subsystem for radiating an illumination light to asurface of an object of inspection mounted on a stage with the objecthaving a plurality of patterns having substantially identical shapeslaid out on the object of inspection; and a detection optical subsystemincluding an image sensor for receiving a light reflected by the objectof inspection and for converting the received light into a detectedimage signal; an image-signal processing unit including a judgment meanswhich forms a judgment as to whether or not a defect exists bycomparison of the image signal output by the detection optical subsystememployed in the image-pickup optical system with a criterion; and anoptical observation microscope provided along with the image-pickupoptical system and used for observation of an optical object on theobject of inspection.

[0045] Furthermore, in the defect inspecting apparatus provided by thepresent invention, the optical observation microscope is implemented byan ultraviolet-ray optical observation microscope.

[0046] Moreover, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection; a detectionoptical system including a photo-electrical conversion means whichreceives a light reflected by the object of inspection and converts thereceived light into a detected signal; and an image-signal processingunit including a means which detects a defect by processing the signaldetected by the detection optical system and outputs a result of thedefect detection including pattern information indicating existence of adefect.

[0047] Further, in the defect inspecting apparatus provided by thepresent invention, the pattern information output by the means employedin the image-signal processing unit is information obtained from designdata of patterns.

[0048] In addition, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection; a detectionoptical system including a photo-electrical conversion means whichreceives a light reflected by the object of inspection and converts thereceived light into a detected signal; and an image-signal processingunit including a means which extracts a signal level of a defect byprocessing the signal detected by the detection optical system, andwhich corrects the extracted defect signal level so as to make thesignal level indicate the size of the defect, and which outputs thecorrected defect signal level.

[0049] Furthermore, the means employed in the image-signal processingunit of the defect inspecting apparatus provided by the presentinvention corrects the signal level of the defect on the basis of theintensity of the illumination light or data representing the reflectanceof the surface of a pattern.

[0050] Moreover, the illumination optical system employed in the defectinspecting apparatus provided by the present invention is configured sothat a light source thereof radiates a slit-shaped beam to a detectionarea on a substrate serving as an object of inspection wherein theslit-shaped beam is formed into a slit-shaped Gaussian beam exhibiting aGaussian illumination distribution having a standard deviationsubstantially equal to a distance from an optical axis of the detectionarea to a periphery.

[0051] Further, the illumination optical system employed in the defectinspecting apparatus provided by the present invention is configured tohave a light source thereof radiate a slit-shaped beam to a detectionarea on a substrate serving as an object of inspection wherein theslit-shaped beam is formed into a slit-shaped Gaussian beam by properlyadjusting a diameter or a major-axis length of the beam to a distancebetween peripheries having the center thereof coinciding with an opticalaxis of the detection area so that a ratio of an illumination at theperipheries of the detection area to an illumination at the center ofthe detection area has a value in the range 0.46 to 0.73.

[0052] In addition, in the defect inspecting apparatus provided by thepresent invention, the slit-shaped Gaussian beam radiated by theillumination optical system is a DUV (Deep Ultra-Violet) beam.

[0053] In the configurations described above, it is possible to detect adefect such as an infinitesimal foreign particle on an inspectedsubstrate, on which repetitive patterns, non-repetitive patterns andnon-patterns coexist with each other, at a high speed and with a highdegree of precision.

[0054] In addition, in the configurations described above, byeffectively utilizing the light quantity of a Gaussian beam radiated byan ordinary inexpensive light source such as a laser-beam source, it ispossible to detect also a defect such as an infinitesimal foreignparticle with a size of the order of 0.1 μm or smaller at a high speedand with a high degree of sensitivity.

[0055] Furthermore, in the configurations described above, byeffectively utilizing the light quantity of a Gaussian beam radiated bytypically a laser-beam source, it is possible to detect also a defectsuch as an infinitesimal foreign particle with a size of the order of0.1 μm or smaller at a high speed and with a high degree of sensitivityby resolving a problem of a lack of illumination at regions surroundingan area on a substrate being inspected due to a decrease in MTF atlocations separated away from an optical axis in a detection opticalsystem.

[0056] Moreover, in the configurations described above, it is possibleto detect a defect such as a real foreign particle by setting the levelof a threshold value at a proper degree of sensitivity withoutsubstantially increasing the amount of generated false informationwherein the threshold value is used as a criterion as to whether or nota defect exists in a variety of circuit-pattern areas in the devicestructure laid out on a substrate being inspected.

[0057] Further, in the configurations described above, it is possible todetect a defect such as a foreign particle with a size to be detected bysetting the level of a threshold value used as a criterion as to whetheror not a defect exists for the size of the defect to be detected in avariety of circuit-pattern areas in the device structure laid out on asubstrate being inspected.

[0058] In addition, in the configurations described above, it ispossible to detect a defect such as a foreign particle by allowing thesize of the defect existing in a variety of circuit-pattern areas in thedevice structure laid out on a substrate being inspected to be inferred.

[0059] Furthermore, in the configurations described above, it ispossible to construct a high-efficiency substrate fabrication line byimplementation of complete inspection and sampling inspection at asufficiently high frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060]FIG. 1 is a diagram showing a semiconductor wafer serving as asubstrate which has memory LSIs laid thereon and is to be inspected by adefect inspecting apparatus implemented by an embodiment of the presentinvention;

[0061]FIG. 2 is a diagram showing a semiconductor wafer serving as asubstrate which has LSIs such as microcomputers laid thereon and is tobe inspected by the defect inspecting apparatus implemented by anotherembodiment of the present invention;

[0062]FIG. 3 is a diagram showing the configuration of a firstembodiment implementing a defect inspecting apparatus provided by thepresent invention in a simple and plain manner;

[0063]FIG. 4 is a block diagram showing the configuration of a secondembodiment implementing an image-signal processing unit employed in thedefect inspecting apparatus shown in FIG. 3;

[0064]FIG. 5 is an explanatory diagram used for describing a methodprovided by the present invention to radiate a slit-shaped beam to asubstrate being inspected such as a semiconductor wafer and a methodprovided by the present invention to detect a beam reflected by thesubstrate;

[0065]FIG. 6 is a diagram showing a squint view of a light beam radiatedby an illumination lens with a conical surface provided by the presentinvention;

[0066]FIG. 7 is an explanatory diagram used for describing a firstembodiment implementing a method to manufacture an illumination lenswith a conical surface provided by the present invention;

[0067]FIG. 8 is an explanatory diagram used for describing a secondembodiment implementing a method to manufacture an illumination lenswith a conical surface provided by the present invention;

[0068]FIG. 9(a) is a diagram showing a side view in the direction of they axis of an illumination optical system provided by the presentinvention and

[0069]FIG. 9(b) is a diagram showing a side view in the direction of thex axis of the illumination optical system provided by the presentinvention;

[0070]FIG. 10 is a diagram showing a top view of an optical subsystemfor radiating slit-shaped beams generated by a single laser-beam sourcein 3 directions to a substrate being inspected such as a semiconductorwafer in the illumination optical system provided by the presentinvention;

[0071]FIG. 11(a) is a diagram showing a birds eye view of radiation anddetection directions according to the present invention whereas

[0072]FIG. 11(b) is a diagram showing a birds eye view of a diffractionlight obtained as a result of reflection of a light radiated in theradiation direction by a pattern;

[0073]FIG. 12 is a diagram showing a relation between: a state ofgeneration of a 0th-order diffraction-light pattern by radiation of aslit-shaped beam in a direction forming an angle of 45 degrees with agroup of main straight lines of a circuit pattern according to thepresent invention; and an aperture of an objective lens employed in adetection optical system with an optical axis thereof oriented in avertical direction;

[0074]FIG. 13 is a diagram showing a relation between: a state ofgeneration of a 0th-order diffraction-light pattern by radiation of aslit-shaped beam in a direction parallel to a group of main straightlines of a circuit pattern according to the present invention; and anaperture of an objective lens, employed in a detection optical systemwith an optical axis thereof oriented in a vertical direction;

[0075]FIG. 14 is a diagram showing a relation between: slit-shaped beamsradiated in 3 different directions each forming an angle of 45 degreeswith a group of main straight lines of a circuit pattern according tothe present invention; and a detection area detected by a TDI imagesensor.

[0076]FIG. 15 is a diagram showing the configuration of a secondembodiment implementing a defect inspecting apparatus provided by thepresent invention in a simple and plain manner;

[0077]FIG. 16 is a diagram showing graphs each representing a relationbetween an angle of emission from a foreign particle and the intensityof a detection signal;

[0078]FIG. 17 is a diagram showing an embodiment wherein an optical axisof a detection optical system is inclined at a gradient and photosensitive surface of a TDI image sensor is inclined at a slope adjustedto the gradient;

[0079]FIG. 18 is a diagram showing a state of projection of adiffraction light beam which is generated by a repetitive pattern when aslit-shaped beam is radiated in a direction forming an angle of 45degrees with a group of main straight lines of a circuit patternaccording to the present invention;

[0080]FIG. 19(a) is a diagram showing a top view of diffraction lightbeams generated by repetitive patterns on a Fourier transformation planeof a detection optical system provided by the present invention; and

[0081]FIG. 19(b) is a diagram showing a relation between the positionsof diffraction light beams and a spatial filter;

[0082]FIG. 20 is a diagram showing relations between: a state ofgeneration of a 0th-order diffraction-light pattern by radiation of aslit-shaped beam in a direction forming an angle of 45 degrees with agroup of main straight lines of a circuit pattern according to thepresent invention; and an aperture of an objective lens of a detectionoptical system with an optical axis thereof oriented in a verticaldirection and the direction of the y axis;

[0083]FIG. 21 is a diagram showing a relation between: a state ofgeneration of a 0th-order diffraction-light pattern by radiation of aslit-shaped beam in a direction parallel to a group of main straightlines of a circuit pattern according to the present invention; and anaperture of an objective lens of a detection optical system with the0th-order diffraction-light pattern not getting in;

[0084]FIG. 22 is a diagram showing an embodiment of the presentinvention wherein a slit-shaped beam with its longitudinal directionoriented in the direction of radiation is radiated to a substrate in adirection forming an angle of 45 degrees with a group of main straightlines of a circuit pattern on the substrate according to the presentinvention;

[0085]FIG. 23 is a diagram showing a special TDI image sensor which isrequired when the slit-shaped beam shown in FIG. 22 is radiated;

[0086]FIG. 24 is a diagram showing a side view of an interference modelof lights scattered by a foreign particle existing on an insulation filmsuch as an oxide film being inspected in accordance with the presentinvention;

[0087]FIG. 25 is an explanatory diagram used for describing anembodiment for detecting lights scattered by a foreign particle existingon an insulation film such as an oxide film in a plurality of detectiondirections in order to detect the foreign particle;

[0088]FIG. 26(a) is a diagram showing a relation between the thicknesschange of an insulation film such as an oxide film and a detectionsignal for an illumination light having a certain wavelength; and

[0089]FIG. 26(b) is a diagram showing a relation between the thicknesschange of an insulation film such as an oxide film and a detectionsignal for illumination lights having 3 different wavelengths;

[0090]FIG. 27(a) is a diagram showing a relation between pixels and awafer used for explaining why it is necessary to compute and set acriterion (threshold value) for extracting a defect such as a foreignparticle in an image-signal processing unit provided by the presentinvention; and

[0091]FIG. 27(b) is a diagram showing a relation between pixels andchips which each have a variety of pattern areas;

[0092]FIG. 28 is a block diagram showing a first embodiment of theimage-signal processing unit provided by the present invention;

[0093]FIG. 29 is a block diagram showing a third embodiment of theimage-signal processing unit provided by the present invention;

[0094]FIG. 30 is a block diagram showing a fourth embodiment of theimage-signal processing unit provided by the present invention;

[0095]FIG. 31 is a block diagram showing a fifth embodiment of theimage-signal processing unit provided by the present invention;

[0096]FIG. 32 is a diagram showing the configuration of a semiconductorfabrication line along which apparatuses for detecting defects such asforeign particles are installed;

[0097]FIG. 33 is an explanatory diagram used for describing the factthat, by increasing the number of various defect inspecting apparatuseswhich are installed along a semiconductor fabrication line and capableof detecting a variety of foreign particles, it is possible to constructa system displaying a high performance as a whole;

[0098]FIG. 34 is a diagram showing changes in yield and defect countthat are observed during a build-up period of mass production;

[0099]FIG. 35 is a diagram showing the configuration of a fourthembodiment implementing a defect inspecting apparatus provided by thepresent invention in a simple and plain manner;

[0100]FIG. 36(a) is a diagram showing an embodiment implementing anillumination optical system employed in the fourth embodimentimplementing a defect inspecting apparatus of FIG. 35 in concrete termsas seen from a position on the y axis; and

[0101]FIG. 36(b) is a diagram showing the same in concrete terms as seenfrom a position on the x axis;

[0102]FIG. 37 is an explanatory diagram used for describing a basicconcept of shaping a slit-shaped Gaussian beam by means of anillumination optical system to increase the illumination efficiency;

[0103] FIGS. 38(a) and 38(b) are explanatory diagrams used fordescribing an image-pickup method to receive a light representing anoptical image in an area of detection on a substrate being inspected byusing a TDI image sensor as a detector;

[0104]FIG. 39 is a diagram showing variations in illumination f(x₀) at aperiphery (x₀=1) of a detection area with changes in standard deviationσ (corresponding to the width of illumination) of a Gaussian Beam;

[0105]FIG. 40 is a diagram showing variations in illumination f(x₀) withchanges in distance x₀ from the optical axis of a detection area for aradiated Gaussian beam at standard deviations σ of 0.5, 1 and 2;

[0106] FIGS. 41(a) and 41(b) are explanatory diagrams used fordescribing an embodiment implementing a TDI image sensor capable ofreceiving a DUV light;

[0107]FIG. 42 is a diagram showing an embodiment of a sequence ofcondition specifying processes in a defect inspecting apparatus providedby the present invention;

[0108]FIG. 43 is a diagram showing a screen displayed on a display meansand used for selecting a condition specifying mode and selecting athreshold value in advance;

[0109]FIG. 44 is a diagram showing a screen appearing on a display meansto show detection sensitivities and detection areas;

[0110]FIG. 45 is a diagram showing a screen appearing on a display meansto show threshold value maps for area-priority, standard andsensitivity-priority modes as well as relations between the sensitivityand the inspection area;

[0111]FIG. 46 is a diagram showing an embodiment implementing a defectinspecting apparatus including a detection optical system having anoptical subsystem for observing a shielded-light pattern of a spatialfilter and an optical-observation microscope;

[0112]FIG. 47 is a diagram showing a relation based on empirical databetween an evaluation value (a level of a detection signal of scatteredlights) and a standard diameter of particles on a reflecting-surfacewafer used in the present invention;

[0113] FIGS. 48(a) and 48(b) are explanatory diagrams used fordescribing an embodiment for inferring the size of a foreign particlefrom a detected image signal;

[0114]FIG. 49 is an explanatory diagram used for describing anembodiment capable of classifying the types of defects from the level ofa signal detected by a laser radiating system and the level of a signaldetected by another radiation system;

[0115]FIG. 50 is a diagram showing the configuration of a defectinspecting apparatus of the present invention including a detectionoptical system and an illumination optical system for radiating a beamby adoption of a bright visual field technique by means of astraight-line-shaped fine mirror;

[0116]FIG. 51 is a diagram showing an embodiment wherein a substrate isinspected for a defect at a high sensitivity prior to processing by aprocess performing apparatus P to produce a pre-processing result A, thesurface is inspected for a defect after the processing to produce apost-processing result B and a logic difference (B-A) is found; and

[0117]FIG. 52 is a diagram showing the configuration of a defectinspecting apparatus provided by the present invention which is capableof forming a judgment as to whether or not a defect exists at high S/Nratios for foreign particles ranging from an infinitesimal defect to adefect exhibiting a spreading characteristic.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0118] Some preferred embodiments of the present invention are explainedby referring to diagrams as follows.

[0119] First of all, an inspection object 1 including a defect such as aforeign particle to be inspected is explained by referring to FIGS. 1and 2.

[0120] A typical inspection object 1 including a defect such as aforeign particle to be detected is a semiconductor wafer 1 a on whichchips 1 aa each to be produced as a memory LSI are laid out2-dimensionally at predetermined intervals as shown in FIG. 1. Each ofthe memory chips 1 aa each to be produced as a memory LSI includesmemory-cell areas 1 ab which occupy a largest region, peripheral-circuitareas 1 ac each including a decoder and a control circuit and otherareas 1 ad. In each of the memory-cell area 1 ab, a repetitive patternof memory cells with a minimum line width of typically about 0.1 to 0.3μm are laid out regularly in 2 dimensions. In a peripheral-circuit area1 ac, on the other hand, a non-repetitive pattern of memory cells with aminimum line width of typically about 0.2 to 0.4 μm are laid outirregularly in 2 dimensions. An example of the other areas 1 ad is abonding area with a minimum line width of typically about 10 μmincluding substantially no pattern.

[0121] Another typical inspection object 1 including a defect such as aforeign particle to be detected is a semiconductor wafer 1 b on whichchips 1 ba each to be produced typically as a microcomputer LSI are laidout 2 -dimensionally at predetermined intervals as shown in FIG. 2. Eachof the chips 1 ba each to be produced typically as a microcomputer LSIincludes main areas such as a register-set area 1 bb, a memory-unit area1 bc, a CPU-core area 1 bd and an input/output-unit area 1 be. It shouldbe noted that FIG. 2 conceptually shows the memory-unit area 1 bc andthe register-set area 1 bb each as a matrix to indicate a repetitivematrix but shows the CPU-core area 1 bd and the input/output-unit area 1be each as a hatched area to represent a non-repetitive pattern. In theregister-set area 1 bb and the memory-unit area 1 bc, a repetitivepattern of elements with a minimum line width of typically about 0.1 to0.3 μm are laid out regularly in 2 dimensions. In the CPU-core area 1 bdand the input/output-unit area 1 be, on the other hand, a non-repetitivepattern of elements with a minimum line width of typically about 0.1 to0.3 μm are laid out irregularly in 2 dimensions.

[0122] As described above, on a semiconductor wafer used as aninspection object 1 including a defect such as a foreign particle to bedetected, chips are laid out regularly. However, a chip has a minimumline width which varies from area to area. In addition, elements in achip may form a repetitive pattern, a non-repetitive pattern or nopattern. Thus, the inspection object 1 can have a variety of possibleforms.

[0123] With the defect inspecting apparatus and the defect inspectionmethod provided by the present invention to detect a defect such as aforeign particle, a 0th-order diffraction light coming from aline-shaped pattern comprising a group of straight lines in anon-repetitive-pattern area in a chip on such an inspection object 1 isprevented from hitting incidence eyes 20 a and 20 c of an objective lensas shown in FIGS. 12 and 21. At the same time, scattered lights comingfrom a defect such as a foreign particle existing in thenon-repetitive-pattern area are received as a detection signal from thedefect such as a foreign particle so that the coordinates of theposition of the defect can be determined.

[0124] In addition, while there may be variations in background signalcaused by subtle differences among processes, which do not indicate adefect, and noise observed in the detection, with the defect inspectingapparatus and the defect inspection method provided by the presentinvention to detect a defect such as a foreign particle, it is possibleto improve the sensitivity to detect a defect such as a foreign particleand the throughput by setting a threshold value used as a criterion inthe extraction of such a defect.

[0125] The following description explains a first embodimentimplementing a defect inspecting apparatus provided by the presentinvention to detect a defect such as a foreign particle by referring toFIGS. 3 and 4.

[0126] As shown in FIG. 3, the first embodiment implementing a defectinspecting apparatus for detecting a defect such as a foreign particlecomprises: a stage unit 300 comprising a substrate mounting base 304, x,y and z stages 301, 302 and 303 and a stage controller 305; 3illumination optical systems 100 having a laser-beam source 101, a beamsplitter comprising a concave lens 102 and a convex lens 103 and anillumination lens 104 having a conical surface; a detection opticalsystem 200 including a detection lens 201, a spatial filter 202, animage formation lens 203, an ND (Neutral Density) filter 207, a beamsplitter 204, a polarization device 208 and one-dimensional detectors(image sensors) 205 and 206 which are each implemented typically by aTDI image sensor; an image-signal processing unit 400 shown in detail inFIG. 4; and a white-color optical system 500 comprising a white-colorlight source 106 and an illumination lens 107.

[0127] In particular, it is desirable to employ a TDI image sensor of ananti-blooming type. By employing a TDI image sensor of an anti-bloomingtype, inspection of a substrate for a defect such as a foreign particlein an area in close proximity to a saturation zone becomes possible.

[0128] As shown in FIG. 4, the image-signal processing unit 400includes: an A/D converter 401; a data memory 402 for delaying a signalby a time to inspect 1 chip of typically a substrate on which chips arealways laid out as a repetitive pattern; a difference processing circuit403 finding a difference between signals coming from chips; a differencememory 404 for temporarily storing differences in signal between chips;a maximum/minimum removing circuit 405 for removing signals representingan abnormal maximum and an abnormal minimum of the differences insignal; a square computing circuit 406 for computing the square of asignal level s; a signal-level computing circuit 407 for computing thesignal level s; a sample counting circuit 408 for counting the number ofsamples; a square integrating circuit 409 for integrating the square ofthe signal level s; a signal-level integrating circuit 410 forintegrating the signal level s; a sample-count computing circuit 411 forcomputing a sample count n for finding a variation; an upper-criterioncomputing circuit (a positive-threshold-value computing circuit) 412; alower-criterion computing circuit (a negative-threshold-value computingcircuit) 413; a comparison circuit 414 for the upper-criterion computingcircuit 412; a comparison circuit 415 for the lower-criterion computingcircuit 413; and a detection-result output means 417 for storing andoutputting a result of detection of a defect such as a foreign particle.

[0129] The image-signal processing unit 400 will be described in detaillater.

[0130] The 3 illumination optical systems 100 have such a configurationthat a light emitted by the laser-beam source 101 passes through thebeam splitter comprising the concave lens 102 and the convex lens 103and then the illumination lens 104 having a conical surface, beingconverted into slit-shaped beams 3 which are radiated to a wafer 1 or aninspected substrate 1 mounted on the substrate mounting base 304 from 3directions 10, 11 and 12 on a plane as shown in FIG. 5 with thelongitudinal directions of the slit-shaped beams 3 oriented to thelayout directions of the chips. It should be noted that the reason whythe light emitted by the laser-beam source 101 is converted into theslit-shaped beams 3 is to realize inspection of a substrate for a defectsuch as a foreign particle at a high speed. That is to say, theslit-shaped beams 3 radiated in the x-axis scanning direction of thex-axis stage 301 and the y-axis scanning direction of the y-axis stage302 to the surface of the wafer 1 on which chips 2 are laid out eachhave a shape resembling a slit which is narrow in the y-axis scanningdirection of the y-axis stage 302 but wide in the vertical direction,that is, the x-axis scanning direction of the x-axis stage 301 as shownin FIG. 5. In this way, the slit-shaped beams 3 are radiated to form animage of the laser-beam source 101 in the direction of the y axis butradiated as parallel beams in the direction of the x axis. It should benoted that the slit-shaped beams 3 can be radiated from the 3 directions10, 11 and 12 individually or radiated in such a way that those from the2 directions 10 and 12 are radiated at the same time.

[0131] By the way, the reason why the longitudinal directions of theslit-shaped beams 3 radiated to the wafer (inspected substrate) 1 areoriented in the layout direction of the chips on the wafer 1perpendicularly to the y-axis scanning direction of the y-axis stage 302is to sustain an integration direction of the TDI image sensors 205 and206 in an orientation parallel to the scanning direction of the stage.In this way, as shown in FIG. 14, an ordinary TDI image sensor can beemployed and, in addition, image signals coming from different chips canbe compared with each other in a simple way. At the same time,coordinates of the position of a detected defect can be found with ease.As a result, is possible to realize inspection of a substrate for adefect such as a foreign particle at a high speed. In particular, theillumination lens 104 having a conical surface is required in order toorient the slit-shaped beams 3 radiated to the wafer (inspectedsubstrate) 1 from the directions 10 and 12 in the layout direction ofchips on the wafer 1 perpendicularly to the y-axis scanning direction ofthe y-axis stage 302.

[0132]FIG. 6 is a diagram showing the illumination lens 104 having aconical surface. The illumination lens 104 has a cylindrical shape withfocal distances varying at locations along the longitudinal direction ofthe cylindrical shape. That is to say, the illumination lens 104 is alens with a linearly varying focal distance. Even if beams are radiatedin a slanting direction at gradients 01 and al as shown in FIG. 6, it ispossible to convert the beams into a slit-shaped beam 3 which isconverged in the direction of the y axis and collimated in the directionof the x axis. That is to say, by using the illumination lens 104, it ispossible to radiate parallel beams in the direction of the x axis asshown in FIG. 9(a) at a gradient φ1 of approximately 45 degrees. Byradiating the parallel slit-shaped beams 3 in the direction of the xaxis as shown in FIG. 9(a), a diffraction-light pattern can be obtainedfrom a circuit pattern with its group of main straight lines oriented inthe directions of the x and y axes, allowing the beams 3 to be shield edby the spatial filter 202.

[0133] Next, a method to manufacture the illumination lens 104 having aconical surface is explained by referring to FIGS. 7 and 8. Made of amaterial such as glass or quartz, a cone 23 having a predeterminedbottom area and a predetermined height is created in a polishingprocess. Then, a lens is cut out from the cone 23 at a predeterminedcross section to make the lens 104 having a conical surface. A curvedsurface of a lens naturally required in the present invention like theone shown in FIG. 6 is actually not a conical surface but must be acurved surface 24 like one shown in FIG. 8. Since the cubic body shownin FIG. 8 is not a not a body symmetrical with respect to an axis ofrotation, however, it is difficult to polish such a body. For thisreason, the lens 104 is approximated by the cone 23 shown in FIG. 7.There will be no problem in practical use provided that the lens has anN. A. in the range 0.02 to 0.2.

[0134] For the shape of the surface of the cone 23 shown in FIG. 7, Eq.(1) given below holds true:

x ² +y ²=(z×tan θ1)²  (1)

[0135] where the symbol θ1 is the vertical angle with the vertex of thecone 23 positioned at the origin.

[0136] As for the curved surface 24 shown in FIG. 8, Eq. (2) given belowholds true:

(x−z×tan θ2)² +y ²=(z×tan θ2)²  (2)

[0137] where the symbol θ2 is likewise the vertical angle with thevertex of the cone 23 positioned at the origin.

[0138] It should be noted that the method of making the conical lens 104is not limited to what is described above. For example, it is alsopossible to adopt another technique such as an injection moldingtechnique whereby a material such as plastic is flowed into a mold witha conical surface made in advance. As another method, there is alsoknown a technique whereby a glass substrate is mounted on a conicalsurface made in advance and the substrate is then melted.

[0139] The conical lens 104 provided by the present invention implementsillumination which is critical in the direction of the y axis andcollimated in the direction of the x axis. Configurations for suchimplementation are shown in FIGS. 9(a) and 9(b). A light emitted by thelaser-beam source 101 is radiated to the conical lens 104 by way of abeam expander comprising the concave lens 102 and the convex lens 103.In the conical lens 104, the light is radiated in a collimated form dueto the fact that there is no lens effect in the direction of the x axis.In addition, since the curvature at one edge of the conical lens 104 isdifferent from the curvature at the other edge, the conical lens 104 hasdifferent focal distances. At the same time, the light is focused on thesurface of the wafer 1 by the curvatures of the conical lenses in thedirection of the y axis.

[0140]FIG. 10 shows a top view of the 3 illumination optical systems 100which employ a single laser-beam source 101. A laser beam emitted by thelaser-beam source 101 is split by an optical splitting element 110implemented typically by a half mirror into 2 paths. A laser beam alongone of the optical paths is reflected by mirrors 111 and 112 beforebeing directed by a mirror 113 downward toward the concave lens 102. Asa result, an illumination beam from a direction 11 is obtained. A laserbeam along the other optical path travels to an optical splittingelement 114 also implemented typically by a half mirror. At the opticalsplitting element 114, the laser beam is further split into to twopaths. A laser beam along one of the optical paths is reflected by amirror 115 before being directed by a mirror 117 downward toward theconcave lens 102. As a result, an illumination beam from a direction 10is obtained. A laser beam along the other optical path is directed by amirror 116 downward toward the concave lens 102. As a result, anillumination beam from a direction 10 is obtained.

[0141] When it is desired to radiate a laser beam to the concave lens102 only from the direction 11, by the way, the optical splittingelement 110 can be replaced by a mirror element 118. When it is desireto radiate laser beams to the concave lens 102 only from the directions10 and 12, on the other hand, the optical splitting element 110 is justremoved from the optical paths or replaced with a proper optical device.Likewise, when it is desired to radiate a laser beam to the concave lens102 only from the direction 12 without the laser beam from the direction10, the optical splitting element 114 can be replaced by a mirrorelement 119.

[0142] It should be noted that, as the laser-beam source 101, it ispossible to employ a high-output YAG laser SHG for generating a secondharmonic wave with a wavelength of 532 nm for a splitting reason eventhough the wavelength does not have to be 532 nm. In addition, thelaser-beam source does not have to be a YAG laser SHG. That is to say,as the laser-beam source 101, it possible to use a source of anotherkind such as an Ar laser, a nitrogen laser, an He—Cd laser or an eximalaser.

[0143] In the detection optical system 200, a light emitted by the wafer1 passes through the detection lens (objective lens) 201, the spatialfilter 202, the image formation lens 203, the ND filter 207, thepolarization device 208 and the beam splitter 204 before being inspectedby the detectors 205 and 206 which are each implemented typically by aTDI image sensor. The spatial filter 202 shield s aFourier-transformation image formed by a diffraction light reflected bya repetitive pattern. The ND filter 207 adjusts the quantity of lightwithout regard to wavelength bands. The spatial filter 202 is placed ina spatial-frequency area of the objective lens 201 at which aFourier-transformation image formed by a diffraction light reflected bya repetitive pattern is to be shield ed. That is to say, the spatialfilter 202 is placed at an image formation position of the Fouriertransformation which corresponds to an emission eye. The polarizationdevice 208 shield s polarization components of reflected scatteredlights which are generated by an edge of a circuit pattern when theillumination optical system 100 radiates a polarization light. However,the polarization device 208 passes some polarization components ofreflected scattered lights which are generated by a defect such as aforeign particle. Thus, the polarization device 208 is not necessarilyrequired by the present invention. In the detection optical system 200,an image of an illuminated area 4 on the wafer 1 shown in FIG. 5 isformed on the detectors 205 and 206 by the image formation lens 203 andthe objective lens 201 serving as a relay lens. That is to say,reference numeral 4 also denotes a photo-sensitive area on the detectors205 and 206 which are each implemented by typically a TDI image sensoras described above.

[0144] When slit-shaped beams 3 are radiated to the wafer (substrate) 1having a variety of circuit patterns formed thereon, reflecteddiffraction lights or scattered lights are emitted from the surface ofthe wafer 1, the circuit patterns and defects such as foreign particles.Each of the emitted lights travels to the detectors 205 and 206 by wayof the detection lens 201, the spatial filter 202, the image formationlens 203, the ND filter 207, the polarization device 208 and the beamsplitter 204. In the detectors 205 and 206, the light is converted intoan electrical signal.

[0145] It should be noted that the shown order in which the ND filter207, the polarization device 208 and the beam splitter 204 are placedalong the optical path is typical. In particular, if the ND filter 207is placed behind the beam splitter 204, the intensities of light beamsarriving at the detectors 205 and 206 can be controlled independently ofeach other.

[0146] In addition, the transmittance and reflectance rates of the beamsplitter 204 do not have to be 50%. For example, the transmittance rateand the reflectance rate can be set at 1% and 99% respectively. Bysetting the transmittance and reflectance of the beam splitter 204 atsuch values that the intensity of the beam hitting one of the detectors205 and 206 is about {fraction (1/100)} of the intensity of the beamhitting one of the other detector in this way, signals will be generatedby the 2 detectors 205 and 206 which receive beams having differentintensities. Thus, the dynamic range of the detectors 205 and 206appears improved. As a result, the image-signal processing unit 400 iscapable of obtaining a detection signal of a defect such as a foreignparticle with an improved dynamic range from signals generated by thedetectors 205 and 206. In particular, a signal generated by one of thedetectors 205 and 206 as a result of a photo-electrical conversion of alight with a large intensity has its a large-intensity componentindicating a defect emphasized. On the other hand, a signal generated bythe other detector as a result of a photo-electrical conversion of alight with a small intensity has its a small-intensity component closeto the background also emphasized. Accordingly, by identifying acorrelation between the 2 emphasized signals such as the ratio of thesignal to the other, the dynamic range of a signal representing a defectcan be enhanced.

[0147] By adjusting the illumination (power) of a beam radiated by thelaser-beam source 101 employed in the illumination optical systems 100,the dynamic range can also be changed. Thus, the beam splitter 204 andone of the detectors 206 can be eliminated.

[0148] The following description explains a relation between theslit-shaped beam 3 radiated by the illumination optical system 100provided by the present invention to the wafer 1 and the detectionoptical system 200 also provided by the present invention in concreteterms. FIG. 5 is a diagram showing a top view of directions ofillumination by the slit-shaped beam 3 and a direction of detection bythe one-dimensional detectors 205 and 206 which are each implementedtypically by a TDI image sensor as described earlier. In the exampleshown in the figure, the slit-shaped beam 3 illuminates the wafer 1 onwhich a pattern 2 is formed. Reference numeral 4 denotes an image formedby the one-dimensional detectors 205 and 206 employed in the detectionoptical system 200. Slit-shaped beams 3 are radiated to the wafer 1 fromdirections 10, 11 and 12 on a plane.

[0149]FIG. 11(a) is an explanatory diagram for supplementing FIG. 5. InFIG. 11(a), reference numeral 10 denotes an illumination direction andreference numeral 14 denotes a detection direction perpendicular to thesurface of a wafer 1 on which the axes x and y are laid. A sphericalsurface 17 is an imaginary surface assumed in thinking of an apertureposition of the objective lens 201 employed in the detection opticalsystem 100 shown in FIG. 5. An illumination light traveling in thedirection 10 and a detection light traveling in the direction 14intersect the spherical surface 17 at cross points 15 and 16respectively.

[0150] On the other hand, FIG. 11(b) is a diagram showing the state ofemission of a diffraction light which is obtained as a result of anillumination in the direction 10. A light resulting from true reflectionof the illumination light in the direction 10 travels in an emissiondirection 19, intersecting the spherical surface 17 at a cross point 18.This light traveling in the emission direction 19 is referred to as a0-order light. Imagine a cone oriented upside down perpendicularly tothe plane of the x and y axes with the vertex thereof coinciding with apoint of illumination on the plane as shown in FIG. 7(b). The beam 3traveling in the illumination direction 10 and the reflected 0th-orderlight traveling in the emission direction 19 form the sides of alongitudinal cross section of the cone. That is to say, a locus of theintersection point of the reflected 0th-order light traveling in theemission direction 19 and the imaginary spherical surface 17 form thecircumference of the bottom of the cone.

[0151] Thus, when seen from the direction of the normal line, the locusis a straight line parallel to the x and y axes.

[0152] By the way, reference numeral 20 a shown in FIGS. 12 and 13denotes the aperture of the objective lens 201 employed in the detectionoptical system 200 which is not inclined or has a gradient β1 of 0.

[0153] In this case, assume that angles φ1 and φ2 formed by theillumination directions 10 and 12 with the y axis respectively are bothset at a typical value of about 45 degrees. With the optical axis of thedetection optical system 200 oriented perpendicularly to the surface ofthe wafer 1, that is, with the gradient β1 set at 0, as shown in FIG. 3,the numerical aperture (N.A.) of the detection lens (objective lens) 201and the angle al of the illumination light shown in FIG. 3 should be setin a range defined by relations (3) shown below with a condition thatthe 0th-order diffraction lights 21 x and 21 y generated by a circuitpattern with its group of main lines thereof oriented in the directionsof the x and y axes respectively are guided not to enter the eye of thedetection lens 201 as shown in FIG. 12. That is to say, by setting theangles φ1 and φ2 formed by the illumination directions 10 and 12 withthe y axis respectively both at a typical value of about 45 degrees andby setting the numerical aperture (N.A.) of the detection lens(objective lens) 201 and the angle α1 of the illumination light shown inFIG. 3 in a range satisfying relations (3) shown below, the 0th-orderdiffraction lights 21 x and 21 y generated by a circuit pattern with itsgroup of main lines thereof oriented in the directions of the x and yaxes respectively can be prevented from entering the aperture 20 a ofthe detection lens 201 even if the circuit pattern is a non-repetitivepattern.

N.A.<cos α1×sin φ1 and

N.A.<cos α1×sin(α/2−φ1)  (3)

[0154] It should be noted that, for al equal to or smaller than 30degrees, the numerical aperture (N.A.) of the objective lens 201 can beset at a value equal to about 0.4 or smaller.

[0155] These conditions are specially effective for products such as aperipheral-circuit area 1 ac having a non-repetitive pattern on a memoryLSI 1 aa, an input/output-unit area 1 be and a CPU-core area 1 bd havinga non-repetitive pattern on an LSI 1 ba such as a microcomputer and alogic LSI having a non repetitive pattern.

[0156] In many cases, LSI patterns are each created in aperpendicular-parallel posture, that is, to contain a group of paralleland perpendicular main straight lines. Thus, 0th-order lights areemitted by these patterns in a specific direction. For this reason, bypreventing the 0th-order lights emitted by these patterns from hittingthe objective lens 201, diffraction lights emitted by most of thesepatterns can be eliminated, making it possible to detect only adiffraction light reflected by a defect such as a foreign particle withease. To put it concretely, there are an increased number of areas whichcontain a defect such as a foreign particle detectable with a highdegree of sensitivity due to the fact that the level of a detectionsignal generated by the circuit pattern is lowered.

[0157] As a mater of course, in the case of a non-repetitive pattern,higher-order (such as the first order, the second order and so on)diffraction lights enter the aperture 20 a of the objective lens 201.Thus, higher-order diffraction lights appear as a group of straightlines parallel to the 0th-order diffraction lights 21 x and 21 y shownin FIG. 12. However, the higher-order diffraction lights can also beeliminated by shield ing the lights by using the spatial filter 202which has a fine band shape.

[0158] In addition, it is necessary to inspect the substrate (wafer) 1for things such as a foreign particle or a defect caught in a dentbetween protrusions like wires or an etching remnant. As describedabove, however, it is also necessary to radiate slit-shaped beams 3having their longitudinal directions oriented in the direction of the xaxis to the substrate 1 being inspected from the directions 10 and 12each forming an angle of about 45 degrees with the y axis in order toprevent a 0th-order diffraction light generated by a non-repetitivepattern existing on the substrate 1 from entering the objective lens201. In this case, things such as protruding wires serve as adisturbance, making it difficult to provide sufficient illumination.

[0159] For the reason described above, in most cases, LSI patterns areeach created in a perpendicular-parallel posture, that is, to contain agroup of parallel and perpendicular main straight lines as describedabove so that, by radiating a slit-shaped beam 3 to the substrate 1 fromthe direction 11 parallel to the y axis, a dent between things such aswires can be illuminated sufficiently. In particular, a wiring patternof a memory LSI is a straight-line pattern with a length of several mmin many cases so that most inspections can be done by illumination fromthis direction 11. In addition, in the case of a 90-degree direction forsome patterns, an inspection can be done by rotating the wafer by 90degrees or by orienting the illumination direction in the direction ofthe x axis.

[0160] When radiating the slit-shaped beam 3 from the direction 11,however, the 0th-degree diffraction light 21 y′ enters the aperture 20 aof the objective lens 201 but the 0th-degree diffraction light 21 x′does not as shown in FIG. 13. It is thus necessary to eliminate this0th-degree diffraction light 21 y′ by shielding the light 21 y′ usingthe spatial filter 202. At that time, as a matter of course, thehigher-order diffraction lights can also be eliminated by shielding thelight 21 y′ using the spatial filter 202.

[0161] The above description explains how to eliminate particularly a0th-order diffraction light reflected by a non-repetitive pattern in thecase of a non-repetitive pattern existing in a chip 2 on the substrate 1being inspected. However, the chip 2 may be a memory LSI 1 aa includinga memory-cell area 1 ab or an LSI 1 ba such a microcomputer including aregister-set area 1 bb and a memory-unit area 1 bc Since the memory-cellarea 1 ab, the register-set area 1 bb and the memory-unit area 1 bc arerepetitive patterns, it is necessary to shield diffraction lights (ordiffracted interference light beams) generated by these repetitivepatterns by using the spatial filter 202. In a word, a repetitivepattern, a non-repetitive pattern and a non pattern coexist with eachother in the chip 2 and, further, the line width varies from pattern topattern. For this reason, a shielding pattern of the spatial filter 202is normally set to eliminate a diffraction light generated typically bya repetitive pattern having a high degree of repetitiveness. Inaddition, in the case of a detection optical system 200 employing aspatial filter 202 with a variable shielding pattern such as onesdisclosed in Japanese Patent Laid-open No. Hei 5-218163 (U.S. Pat. No.5,463,459) and Japanese Patent Laid-open No. Hei 6-258239, the shieldingpattern is changed in accordance with a circuit pattern of the chip 2.As an alternative, a plurality of spatial filters 202 with differentshielding patterns are provided in advance and one of them appropriatefor the circuit pattern in the chip 2 is selected.

[0162] The following description explains how to adjust the detectionsensitivity in accordance with the size of a defect such as a foreignparticle to be detected. That is to say, the detection sensitivity isexpected to increase even at the expense of a lower throughput byreducing the size of the detection pixel on the inspection object 1 ofthe one-dimensional detectors (image sensors) 205 and 206 which are eachimplemented by typically a TDI image sensor as described above. Thus,when detecting a defect such as a foreign particle with a dimension notexceeding 0.1 μm, the defect inspecting apparatus is switched to adetection optical system 200 which decreases the pixel size. To put itconcretely, it is desirable to provide 3 detection optical systems ofdifferent types typically appropriate for respectively images with sizesof 2 μm, 1 μm and 0.5 μm on the wafer 1 for pixels such as those of theTDI image sensors. As a technique of implementation of the detectionoptical system 200, the entire optical system 200 can be replaced byanother one, or only the lens (group of lenses) 203 or the lens (groupof lenses) 201 is replaced. In this case, the configurations of thelenses may be designed so that the switching can be done withoutchanging the lengths of the optical paths between the wafer 1 and theone-dimensional detectors 205 and 206 which are each implemented bytypically a TDI image sensor as described above. If the design isdifficult, it is also possible to use a mechanism which tolerateschanges in distances to the sensors accompanying switching of thedetection optical system 200 from one lens to another. As anotheralternative, the detection optical system 200 can also be switched fromone lens to another with a different pixel size of the sensor itself.

[0163] The following description explains a concrete embodiment of arelation between the slit-shaped beams 3 radiated from the 3 directionsand the TDI image sensors 205 and 206 by referring to FIG. 14. FIG. 14is a diagram showing a relation between a TDI image 4 on the wafer 1 andslit-shaped beams 3-10 and 3-12 radiated from the directions 10 and 12respectively. When beams obtained as a result of splitting a laser beamgenerated by a single laser-beam source 101 are radiated from thedirections 10 and 12 as shown in FIG. 10, the beams interfere eachother, resulting in variations in intensity in the illumination zone. Inorder to solve this problem, the beams 3-10 and 3-12 are radiated insuch a way that they do not interfere each other in the zone of the TDIimage 4 as shown in FIG. 14 in order to eliminate effects of theinterference. When the TDI image sensors 205 and 206 are used, theproblem caused by such a positional shift does not arise since detectionoutputs in the zone of the image 4 are integrated in the direction ofthe y axis in the zone in synchronization with the movement of they-axis stage. Also when the slit-shaped beam 3-11 radiated from thedirection 11 is used, the beams 3-10, 3-11 and 3-12 are similarlyradiated so that they do not interfere each other in the zone, causing aproblem of an overlap of the 3 beams. It is needless to say that theproblem of interference can be avoided in the same way for any 2 of the3 slit-shaped beams 3-10, 3-11 and 3-12 radiated from the directions 10,11 and 12 respectively.

[0164] As shown explicitly in none of the figures, when the slit-shapedbeams 3-10 and 3-12 are radiated from the directions 10 and 12respectively to the same location, they will interfere each other. Sincethe interfering beams are inclined in the direction of the y axis,however, variations in illumination intensity caused by the interferenceare reduced by an effect of an integration carried out by the TDI imagesensors 205 and 206. It is thus not necessary to radiate the slit-shapedbeams 10 and 12 so-that they do not interfere each other as shown inFIG. 14.

[0165] The following description explains a second embodimentimplementing a defect inspecting apparatus provided by the presentinvention for detecting a defect such as a foreign particle by referringto FIG. 15. As shown in the figure, in order to increase the intensityof a scattered light coming from a defect such as a foreign particle,the optical axis of the detection optical system 200 is inclined by anangle β1 from the vertical direction. The rest of the configuration isthe same as the first embodiment shown in FIG. 3.

[0166] The reason why the optical axis of the detection optical system200 is inclined by an angle β1 from the vertical direction is toincrease the intensity of a scattered light coming from a defect such asa foreign particle as shown in FIG. 16 and, hence, to increase thedetection sensitivity. The increase in light intensity is attributed tothe following cause. A particle or a foreign particle larger in sizethan a fraction of the illumination wavelength generates a light 51 witha high intensity scattered in the forward direction. On the other hand,a light 52 generated by an area such as a dry spot with a size close to{fraction (1/10)} of the wavelength or smaller is scattered almost inthe forward direction so that the intensity of the scattered light fromthe infinitesimal particle in the forward direction is relatively high.As a result, if there are a plurality of dry spots on the surface of acircuit pattern among detection pixels, the total intensity isrepresented by a curve 53 shown in FIG. 16. Thus, by taking thescattered lights traveling in the forward direction, an infinitesimalparticle or a defect can be detected from a surface dry spot.

[0167] If TDI (Time Delay Integration) sensors are used as the detectors205 and 206, however, the optical axis of the detection optical system200 can not be inclined due to a focal depth. Thus, in the case of thesecond embodiment, one-dimensional sensors are employed. As analternative, the magnification of a set comprising the detection lens201, the spatial filter 202 and the image formation lens 203 employed inthe detection optical system 200 is doubled or increased by severaltimes and, as shown in FIG. 17, the TDI image sensors 205 and 206 areinclined at a gradient β2 expressed by Eq. (4) below. In this way, themagnification can be adjusted for the entire surface.

tan β2=M×tan β1  (4)

[0168] where the symbol M denotes the magnification of the setcomprising the detection lens 201, the spatial filter 202 and the imageformation lens 203.

[0169] It should be noted that, if one-dimensional sensors are employed,the inclination at the gradient β2 is not required.

[0170] The next description explains detection of scattered lightsgenerated by a defect such as a foreign particle using theone-dimensional detectors 205 and 206 each implemented typically by aTDI image sensor by elimination of diffraction lights generated by anon-repetitive pattern and a repetitive pattern in the secondembodiment. Also in the case of the second embodiment, slit-shaped beams3 are radiated to the substrate (or wafer) 1 being inspected in the sameway as that shown in FIG. 5. When a slit-shaped beam 3 is radiated fromthe direction 10 as shown in FIG. 11(a), the state of emission of adiffraction light generated by the substrate 1 is shown in FIG. 11(b) asis the case with the first embodiment. That is to say, a light resultingfrom true reflection of the illumination light in the direction 10travels in the emission direction 19, intersecting the virtual sphericalsurface 17 at the cross point 18, and the light traveling in theemission direction 19 is referred to as a 0th-order light. The beam 3traveling in the illumination direction 10 and the reflected 0th-orderlight traveling in the emission direction 19 form the sides of alongitudinal cross section of an imaginary cone oriented upside downperpendicularly to the plane of the x and y axes with the vertex of thecone coinciding with a point of illumination on the plane. Thus, a locusof the intersection point of the reflected 0th-order light traveling inthe emission direction 19 and the imaginary spherical surface 17 formthe circumference of the bottom of the cone as shown in FIG. 18.Accordingly, in the case of a repetitive pattern, when seen from thedirection of the normal line, the locus of the 0th-order light is astraight line parallel to the x and y axes.

[0171] In particular, in the case of a repetitive pattern, the localmaximum of the 0th-order diffraction light is located at an intersectionpoint 22 of the group of straight lines. Thus, the aperture 20 b of theobjective lens 201 employed in the detection optical system 200 inclinedat a gradient β1 is like one shown in FIG. 18. When the aperture 20 b isseen from a direction 14, that is, the direction of the optical axis,the 0th-order diffraction light 22 appears to be emitted to anintersection point of a curve and a straight line shown in FIG. 19(a).

[0172] Then, by shield ing these diffraction lights by means of ashielding portion 207 having a straight-line shape like one shown inFIG. 19(b) in the spatial filter 202, a signal generated by a patterncan be removed. In addition, if the shape and the pitch of a repetitivepattern on the wafer 1 change, the pitch of the locus of the directionsof the x and y axes changes, centering at an emission point 18 shown inFIG. 18. Thus, in the aperture 20 b, the pitch and the phase of thediffraction light 22 change. In order to shield these diffractionlights, it is necessary to change the pitch and the phase of thestraight-line-shaped shielding portion 207.

[0173] As described above, a diffraction light generated by a repetitivepattern can be shielded by the spatial filter 202.

[0174] The next description explains elimination of diffraction lightsgenerated by a non-repetitive pattern. In general, a non-repetitivepattern is a straight-line pattern oriented in the directions of the xand y axes. Thus, when a slit-shaped beam 3 is radiated from thedirection 10, 0th-order diffraction lights 21 x and 21 y in thedirections of the x and y axes respectively shown in FIG. 20 aregenerated as is the case shown in FIG. 12. Since the optical axis 200 ofthe detection optical system 200 is inclined at the gradient 31,however, the intensity of a light scattered by an infinitesimal particleis high but the 0th-order diffraction light 21 x emitted in thedirection of the y axis enters the aperture 20 b of the objective lens201. Thus, also in the case of a non repetitive pattern, it becomesnecessary to shield the 0th-order diffraction light 21 x by using thespatial filter 202.

[0175] Since a diffraction light beam generated by a repetitive patternis different from a 0th-order diffraction light pattern for anon-repetitive pattern as described above, it is necessary to provideboth the diffraction-light patterns to the spatial filter 202. If anattempt is made to shield both the diffraction-light patterns by usingthe spatial filter 202, however, the intensity of a scattered lightpassing through the spatial filter 202 is attenuated, causing thesensitivity to deteriorate.

[0176] In order to solve the problem described above, the optical axisof the detection optical system 200 is erected to position the apertureof the objective lens 201 at a location 20 a and to radiate slit-shapedbeams 3 to a non-repetitive pattern from the directions 10 and 12 as isthe case with the first embodiment. In this way, 0th-order lightpatterns 21 x and 21 y can be prevented from entering the aperture 20 aof the objective lens 201, making it possible to detect a defect such asa foreign particle existing on a non-repetitive pattern.

[0177] As is obvious from the description of the first embodiment givenearlier, however, it is necessary to radiate a slit-shaped beam 3 fromthe direction of the y axis 11 as shown in FIG. 13 in an attempt todetect a defect such as a foreign particle existing in a dent betweenwires. In this case, however, a 0th-order diffraction light 21 y′ entersthe aperture 20 a of the objective lens 201 as shown in FIG. 13, makingit necessary to shield the light 21 y′ by means of the spatial filter202. Nevertheless, the detection of a defect such as a foreign particleexisting in a dent between wires is not the principal part of thedetection of defect in general including foreign particles. Since apattern being inspected is identified, a measure can be taken during theimage processing.

[0178] If the conditions described above are configured in a waydescribed below, the conditions can be satisfied. To put it in detail,the illuminations from the directions 10 and 12 each forming an angle of45 degrees with the y axis are given up and only a slit-shaped beam 3 isradiated from the direction of the y axis 11. The optical axis of thedetection optical system 200 is inclined from the vertical directiontoward the directions of the x and y axes to place the aperture of theobjective lens 201 at a position denoted by reference numeral 20 c inFIG. 21. In this way, 0th-order light patterns 21 x′ and 21 y′ can beprevented from entering the aperture 20 c of the objective lens 201. Inthis configuration, the spatial filter 202 can be designed to shieldonly a diffraction light beam generated by a repetitive pattern. Inaddition, it is possible to prevent deterioration of the intensity of ascattered light passing through the spatial filter 202 from a defectsuch as a foreign particle.

[0179] In this case, however, it is necessary to decrease the N.A. ofthe objective lens 201.

[0180] The problem is the focuses of the detectors 205 and 206. As shownin FIG. 17, the configuration with the inclined detectors 205 and 206allows the focuses to be adjusted in the entire image formation area. Inthis case, it will be insufficient to merely incline the detectors 205and 206 at a gradient β2. Instead, it is necessary to incline them atthe gradient β2 and in a direction perpendicular to the direction 14. Inaddition, since the detection optical system 200 employs a telecentricoptical system, the horizontal magnification by no means changes at aportion where the focal positions are different from each other.

[0181] Next, the following description explains a third embodimentimplementing a defect inspection apparatus provided by the presentinvention for detecting a defect such as a foreign particle. The thirdembodiment is inferior to the first and second embodiments.

[0182] In the case of the third embodiment, a cylindrical lens 104′ isemployed in place of the conical lens 104 as shown in FIG. 22. By usingthe cylindrical lens 104′, slit-shaped beams 3′ with the longitudinaldirections thereof oriented to the illumination directions 10 and 12 areradiated to the surface of the wafer 1. The illumination directions 10and 12 are inclined from the layout direction of chips created on thewafer 1 by an angle of about 45 degrees. The slit shapes of the beamsare parallel to the incidence plane of the illumination. As a matter ofcourse, since the slit-shaped beams 3′ are beams parallel to each otherin their longitudinal direction, they do not intercept each other in thetransversal direction. It should be noted that diffraction lightsgenerated by repetitive and non-repetitive patterns created on chips 2on the wafer 1 are handled in the same way as the first and secondembodiments.

[0183] In the case of the third embodiment, it is necessary to set they-axis scanning direction of the stage in an orientation perpendicularor parallel to the chips in order to make chip comparison simple. Inaddition, since the integration direction of the TDI image sensors isnot parallel to the y-axis scanning direction of the stage in the thirdembodiment, TDI image sensors can not be used as the detectors 205 and206. It is thus necessary to employ one-dimensional linear sensors asthe detectors 205 and 206. In the case of a linear sensor, since anoptical signal from an area narrower than the width of the illuminationbeam is detected, it is desired to squeeze the illumination beam 3′ to awidth close to the image 4 of the sensor in order to utilize theillumination beam 3′ with a high degree of efficiency. To put itconcretely, assume that the pixel size of the sensor is 13 μm and themagnification of the optical system is 6.5 times. In this case, thepixel size of the image of the sensor formed on the wafer 1 is 2 μm. Letthe wavelength of the used laser be 532 nm. In this case, it isdesirable to set the N.A. (numerical aperture) of the lens 104′ employedin a direction perpendicular to the longitudinal direction of the sensorat about 0.5 in Eq. (5) given below. Of course, this value is selectedonly in order to increase the efficiency of the illumination. If it isnot necessary to increase the efficiency of the illumination, a smallerN.A. can be used.

d=1.22×λ/N.A.  (5)

[0184] where the symbol d denotes the half band width and the symbol λdenotes the wavelength of the illumination beam.

[0185] When TDI image sensors are used as the detectors 205 and 206 inthe method of illumination shown in FIG. 22, the sensors must bespecial, having a shape like one shown in FIG. 23. That is to say, thespecial TDI image sensors have a pixel configuration with an integrationdirection inclined at a gradient φ1.

[0186] The following description explains detection of a defect such asa foreign particle existing on an insulation film such as an oxide filmwith no pattern used as an object of inspection.

[0187]FIG. 24 is a diagram showing a state of scattering of lights by atransparent film such as an oxide film. Assume that a very smallinfinitesimal particle or a foreign particle 34 with a size equal to afraction of the wavelength of the illumination beam exists on thesurface of an oxide film 32 on a substrate 33. In this case, theparticle generates a beam having a spherical polarization plane. That isto say, a beam is radiated to the surface of the oxide film 32 and tothe detectors at the same time. The beam emitted by a particle with sucha polarization plane is a result of reflection of the beam radiated tothe oxide film 32 by a boundary surface between the oxide film 32 and anunderlying layer 33. The reflected beam interferes the beam radiateddirectly to the defector, resulting in strength in the emissiondirection. As a result, outputs of the detection in directions 36, 37and 38 are different from each other. The intensity distribution changesin dependence on the thickness of the oxide film and the refractiveindex. As a result, the intensity of a detection beam detected from thesame direction changes, causing the sensitivity to also vary as well.

[0188] According to consideration based on this model, however, theoutput of a detected light remains unchanged without regard to thedirection of the illumination. In addition, experiments have proven thatthe output of a detected beam does not change even if the angle ofincidence of the illumination light is changed.

[0189] However, optical interference can be eliminated by radiation of awhite light. As a matter of fact, the first and second embodiments areprovided with a white-illumination optical system 500 for detecting aforeign particle on the insulation film 32 such as an oxide film. Thus,in order to detect a foreign particle on the insulation film 32, thewhite-color light source 106 is turned on while the laser-beam source101 is turned off. In addition, white-color illumination is also adoptedfor an object of inspection affected by the wavelength of theillumination light.

[0190] In the case of white-color illumination, the resultingillumination spot is bigger in size than the visual field of the TDIimage sensors.

[0191] In addition, when the laser-beam source 101 is used forgenerating an illumination light, it is necessary to employ an objectivelens 201 with a large numerical aperture in order to stabilize thedetection output on the oxide film 32. This is because such an objectivelens 201 is capable of detecting most lights emitted from the surface ofthe wafer 1. If an objective lens 201 with a small numerical aperture isused, on the other hand, a plurality of such lenses 201 are required. Inthis case, detection outputs of the lenses 201 are integrated. As analternative, a plurality illumination lights with different wavelengthsare used and their results of detection are integrated.

[0192] In this case, absorption or attenuation of a scattered lightgenerated by a foreign particle on the film can be assumed to besubstantially non-existent. In the case of a non-existing foreignparticle, lights are emitted in one direction so that, the output inthis direction varies due to interference. If a foreign particle exists,on the other hand, the emitted light is spread in a plurality ofemission directions since interference occurs in the form of intensitydistribution among the emission directions.

[0193]FIG. 25 is a diagram showing the configuration of an embodimentfor detection from a plurality of directions. From lights emitted indirections 213, 214 and 215, detection lenses 210, 211 and 212 formimages which are detected by detectors 213, 214 and 215 respectively.Analog electrical signals obtained as results of photo-electricalconversions carried out by the detectors 213, 214 and 215 are convertedinto digital data by A/D converters 451, 452 and 453 respectively. Thedigital data is then integrated by an integration means 454 andconverted into binary data representing a result of detection by using aproper threshold value.

[0194] It should be noted that the number of detection systems includingthe detection lenses 210, 211 and 212 does not have to be 3. Forexample, 2 detection systems are OK. In addition, the detection systemsin this embodiment are each implemented by the detection optical system200 shown in FIG. 3. In this case, each of the detection optical systems200 is inclined by a gradient β. Examples of the gradient are β1=0degrees and β1=45 degrees.

[0195]FIG. 26 is diagrams showing changes in detection signal withvariations in oxide-film thickness. To be more specific, FIG. 26(a) is adiagram showing an intensity-variation change 48 of a light with acertain wavelength. On the other hand, FIG. 26(b) is a diagram showingintensity-variation curves 48, 49 and 50 of 3 lights with differentwavelengths. By integrating results of detection for the lights withdifferent wavelengths shown in FIG. 26(b), variations in integrationresult will be smaller than variations in intensity shown in FIG. 26(a)as is obvious from the figures.

[0196] In this case, since we know that the intensity of a detectedsignal is not dependent on the angle of incidence of the illuminationlight, lights with different wavelengths can be radiated at differentangles of incidence or from different directions determined by the angleφ. That is to say, by setting the wavelengths of the slit-shaped beams 3radiated from the directions 10, 11 and 12 at values different from eachother, it is possible to detect a signal indicating a foreign particleon an insulation film such as an oxide film by means of a singledetection optical system 200. The reason why it is possible to detect asignal indicating a foreign particle on an insulation film such as anoxide film by means of a single detection optical system 200 by settingthe wavelengths of the slit-shaped beams 3 radiated from the directions10, 11 and 12 at values different from each other is that there is nomutual interference. As a result, it is possible to avoid an increase incost caused by a need to prepare a plurality of detection opticalsystems 200. With at least 2 beams having different wavelengths, thedetection optical system 200 is capable of correcting color aberration(and a focal distance) with ease. As a result, there is no difficulty inthe implementation as long as 2 beams having different wavelengths areused.

[0197] The next description explains a fourth embodiment implementing adefect inspecting apparatus provided by the present invention fordetecting a defect such as a foreign particle. By the way, withsemiconductor devices miniaturized more and more, a further increase inyield is also required. To put it in detail, a circuit pattern createdon a semiconductor substrate such as a semiconductor wafer for makingsuch semiconductor devices is subjected to super miniaturization with adesign rule of 0.3 to 0.2 μm or even smaller. For this reason, a foreignparticle existing on the semiconductor substrate causes a semiconductordevice created on the substrate to operate abnormally even if theforeign particle is an infinitesimal molecule with a size of about 0.1μm or smaller or a particle with a size close to that at an atomiclevel.

[0198] In such a state of the art to fabricate a semiconductor device,the defect inspecting apparatus provided by the present invention fordetecting a defect such as a foreign particle is required to have acapability of inspecting a defect such as an infinitesimal foreignparticle existing on a semiconductor substrate such as a semiconductorwafer, on which a circuit pattern undergoing a super-miniaturization bya design rule of 0.3 to 0.2 μm or even smaller exists, with a highdegree of sensitivity at a high speed.

[0199]FIG. 35 is a diagram showing the fourth embodiment implementing adefect inspecting apparatus provided by the present invention fordetecting a defect such as a foreign particle in a simple and plainmanner. FIG. 36 is a diagram showing an embodiment implementing anillumination optical system employed in the defect inspecting apparatus.

[0200] As shown in FIG. 35, the defect inspecting apparatus fordetecting a defect such as a foreign particle comprises: stages 301, 302and 303 for mounting an inspection object 1 such as a semiconductordevice or a semiconductor wafer on which a super-miniaturized circuitpattern with a defect thereof to be detected has been created; anillumination-light source 101 implemented by a laser-beam source such asa semiconductor laser, an argon laser, a YAG-SHG laser or an eximalaser; an illumination optical system comprising the components 102 to105 for radiating a high-luminance light emitted by theillumination-light source (laser source) 101 to an illumination area 3on the inspection object 1 from a slanting direction as a slit-shapedGaussian beam 107 having a illumination distribution close to theGaussian distribution as shown in FIG. 37; a detection optical system200 including a detection lens (objective lens) 201, a spatial filter202, an image formation lens 203, an ND filter 207 and a beam splitter204 which are used for forming an image from diffraction lights (orscattered lights) reflected by a detection area 4 to pass through thedetection optical system 200; detectors 205 and 206 each implementedtypically by a TDI image sensor or a CCD image sensor having aphoto-sensitive surface corresponding to the detection area 4; and animage-signal processing unit 400 for detecting a defect such as aforeign particle from an image signal output by the detectors 205 and206.

[0201] It should be noted that the defect inspecting apparatus also hasan automatic focus control system for controlling formation of an imageof the surface of the inspection object 1 on the photo-sensitive surfaceof the detectors 205 and 206.

[0202] The actual configuration of the illumination-light optical source101 and the illumination optical systems comprising the components 102to 105 is shown in FIG. 36. In the figure, reference numeral 102 denotesa concave or convex lens for enlarging the diameter of a laser beam 1006emitted by the illumination-light source 101. Reference numeral 103denotes a collimate lens for converting a laser beam output by theconcave or convex lens 102 with an expanding diameter into substantiallyparallel beams. Reference numeral 104 denotes an illumination lens witha conical surface for converging the substantially parallel beamsobtained as a result of the conversion in the collimate lens 103 in thedirection of the y axis and for radiating the converged beams to anillumination area 3 on the inspection object 1 as a slit-shaped Gaussianbeam 1007 having an illumination distribution close to the Gaussiandistribution as shown in FIG. 37. The illumination lens 104 serves as anoptical system having a converging function in the direction of the yaxis.

[0203] It should be noted that the concave or convex lens 102 and thecollimate lens 103 constitute a beam expander for enlarging the diameterof the laser beam 1006. Thus, the illumination optical system includingthe components 102 to 104 can be regarded as a system comprising thebeam expander, the conical lens 104 and a mirror. The beam expandertypically comprises a collimate lens, a concave lens and a receiverlens. As described above, the conical lens 104 is used for convergingthe substantially parallel beams obtained as a result of the conversionin the beam expander in the direction of the y axis and for radiatingthe converged beams to an illumination area 3 on the inspection object 1as a slit-shaped Gaussian beam 1007 having an illumination distributionclose to the Gaussian distribution as shown in FIG. 36. The mirrorreflects the slit-shaped Gaussian beam 1007 output by the conical lens104 and radiates the beam 1007 to the inspection object 1 in a slantingdirection.

[0204] By the way, by changing the distance b between the concave orconvex lens 102 and the collimate lens 103 or the distance between theconcave lens and the receiver lens in the configuration described above,the x-direction width of the luminance beam having an illuminationdistribution substantially resembling the Gaussian distribution can bealtered. That is to say, by adjusting the beam expander, the x-directionlength Lx of the illumination area 3 (or the slit-shaped beam 1007)having an illumination distribution substantially resembling theGaussian distribution can be changed. In addition, by varying thedistance between the conical lens 104 and the inspection object 1, they-direction length Ly of the illumination area 3 (or the slit-shapedbeam 1007) having an illumination distribution substantially resemblingthe Gaussian distribution can also be changed.

[0205] A detection area 4 shown in FIG. 37 is an area on the inspectionobject 1 to be inspected by using a TDI image sensor or a CCD imagesensor. In the case of a TDI image sensor, for example, the dimensionsof each pixel are typically 27 μm×27 μm. The TDI image sensor istypically a 64×4,096 CCD image-pickup sensor which comprises 64 rows inthe TDI (Time Delay Integration) direction and 4,096 columns in the MUXdirection, and operates in a TDI mode. That is to say, the TDI imagesensors 205 a and 206 a have a configuration comprising n stages of linesensors as shown in FIG. 38 where n is typically 64. A line rate rt isthe amount of information output by the sensor which is the line sensorsin this case. At a line rate rt, accumulated charge is transferredthrough lines 1, 2 and so on, from one line to another. By synchronizingthe movement speed of the y-axis stage 302 for moving the inspectionobject 1 in the direction of the y axis with the line rate rt, an image6 based on a scattered light and a diffraction light generated bytypically an infinitesimal foreign particle 5 is accumulated for a longtime it takes to transfer the charge to the line n so that a defect suchas an infinitesimal foreign particle can be detected with a high degreeof sensitivity. In this image sensor, the image of a defect such as aninfinitesimal foreign particle is detected as a sum of intensities of ascattered light and a diffraction light traveling from the line 1 to theline n. However, a scattered light or a diffraction light coming fromthe same point on the object of inspection and reaching the lines istimewise entirely incoherent.

[0206] As described above, a beam emitted by the illumination-lightsource 101 is converted by the illumination optical system (or theradiation optical system) comprising the components 102 to 104 into aslit-shaped Gaussian beam 1007 which is radiated to the surface of theinspected substrate 1 on the stages 301 to 303 typically in a slantingdirection to form an illumination area 3 on the surface. While theinspected substrate 1 is being moved in the direction of the y axis bymoving the y-axis stage 302 in the direction of the y axis, thedetectors 205 a and 206 a each implemented typically by a TDI imagesensor transfers electric charge accumulated in each pixel from one lineto another at a line rate rt synchronized with the movement speed of they-axis stage 302. In this way, while an optical image of the detectionarea 4 on the inspected substrate 1 formed by the detection opticalsystem comprising the components 201 to 204 is being picked up, eachpixel (or each device) along the width H of the detection area 4 isscanned to generate a detection signal which is then supplied to theimage-signal processing unit 400. By processing the detection signal inthe image-signal processing unit 400, it is possible to detect a defectsuch as an infinitesimal foreign particle existing in the detection area4 with a high degree of sensitivity and at a high speed.

[0207] By using the TDI image sensors 205 a and 206 a as describedabove, it is possible to compute a total of illumination values of ascattered light or a diffraction light generated by a defect such as aninfinitesimal foreign particle where (quantity of light =illuminationvalue x time) and, hence, to increase the sensitivity. In addition, oncethe slit-shaped beam 1007 is radiated to the radiation area 3 and, alight generated by the detection area 4 is received by the TDI imagesensors 205 a and 206 a while the inspected substrate 1 is being movedin the direction of the y axis in synchronization with the line rate rtof the TDI image sensors so that it is possible to detect a defect suchas an infinitesimal foreign particle existing in the detection area 4with a large width H at a high speed.

[0208] The following description further describes the fourth embodimentof the present invention for detecting a defect such as an infinitesimalforeign particle with a size of about 0.1 μm or smaller with a highdegree of sensitivity and at a high speed. That is to say, when it isdesired to detect a defect such as an infinitesimal foreign particlewith a size of about 0.1 μm or smaller with a high degree ofsensitivity, it is necessary to increase the intensity of a scatteredlight or a diffraction light generated by a defect such as aninfinitesimal foreign particle and received by pixels of a TDI imagesensor 302 a and also to reduce the dimensions of each pixel on theinspected substrate 1 to about 1 μm×1 μm or smaller.

[0209] It is possible to realize an implementation wherein thedimensions of each pixel on the inspected substrate 1 are reduced toabout 1 μm×1 μm or smaller as described above by setting the imageformation magnification M of the detection optical system comprising thecomponents 201 to 204 including an objective lens at a value of about 27times or larger for dimensions of each pixel on the TDI image sensors oftypically 27 μm×27 μm. It should be noted that, if 26×4,096 CCD pickupsensors are used as the TDI image sensors 205 a and 206 a, the detectionarea 4 will have a width W not exceeding a value of about 26 μm and aheight H not exceeding a value of about 4,096 μm.

[0210] In addition, the detection optical system comprising thecomponents 201 to 204 for forming an image in photo-sensitive areas onthe TDI image sensors 205 a and 206 a from an optical image formed by ascattered light or a diffraction light generated by the surface of theinspected substrate 1 includes an objective lens having a characteristicwhich, due to lens aberration, shows the fact that, the farther aposition from the center of the lens (or the optical axis 2001), thatis, the closer a position to a periphery, the smaller the MTF(Modulation Transfer Function) at the position. The MTF representschanges in contrast of an image of a sinusoidal wave pattern as afunction of spatial frequency. For this reason, it is necessary toincrease the intensity of a scattered light or a diffraction lightgenerated by pixels 205 ae and 206 ae on the edge (or the periphery)with a smallest MTF located farthest from the optical axis 2001 on thephoto-sensitive surface of the TDI image sensors 205 a and 206 a shownin FIG. 38(a), or generated by a defect such as an infinitesimal foreignparticle located on the edge (or the periphery) with a smallest MTFfarthest from the optical axis 2001 in the detection area 4 shown inFIG. 37.

[0211] By the way, the illumination of the slit-shaped Gaussian beam1007 radiated to the radiation area 3 on the surface of the inspectedsubstrate 1 by the illumination-light source 101 and the illuminationoptical system comprising the components 102 to 104 exhibits theordinary Gaussian distribution as shown in FIG. 37, wasting illuminationoutside the detection area 4. On the other hand, it is necessary toilluminate the illumination area 3 which is made larger than thedetection area 4.

[0212] In order to solve this problem, in this present invention, thequantity of a light emitted by the illumination-light source 101 isutilized effectively and the illumination on the edge (or the periphery)with a smallest MTF farthest from the optical axis 2001 in the detectionarea 4 is increased most without increasing the illumination of thelight in order to detect a defect such as an infinitesimal foreignparticle with a size of about 0.1 μm or smaller with a high degree ofsensitivity. That is to say, by employing a low-cost illumination-lightsource 101 for emitting a light with a minimum required illumination,the illumination on the edge (or the periphery) with a smallest MTFfarthest from the optical axis 2001 in the detection area 4 can beincreased most by the illumination optical system comprising thecomponents 102 to 104 to implement illumination with a high degree ofefficiency. Examples of such a low-cost illumination-light source 101are a laser-beam source such as a semiconductor laser, an argon laser, aYAG-SHG laser or an exima laser and a filament light source such as acanon lamp, an electric-discharge tube such as mercury lamp and ahalogen lamp.

[0213] To put it concretely, in the present invention, when theillumination-light source 101 and the illumination optical systemcomprising the components 102 to 104 radiates a slit-shaped beam 1007having an illumination of the Gaussian distribution to illuminate theillumination area 3 on the inspected substrate 1, the illuminationoptical system comprising the components 102 to 104 is adjusted (orcontrolled) to set such a width of the illumination that theillumination on the periphery of the detection area 4 is maximized. TheGaussian distribution of the illumination of the slit-shaped beam 1007shown in FIG. 37 can be expressed by Eq. (6) given below. Theillumination on the periphery of the detection area 4 is maximized whenthe expression on the right-hand side of Eq. (7) is equal to 0.$\begin{matrix}{{f\left( X_{0} \right)} = {\frac{1}{\sqrt{2{\pi\sigma}}}{\exp \left( {{- \frac{1}{2\sigma^{2}}}X_{0}^{2}} \right)}}} & (6) \\{\frac{\partial{f\left( X_{0} \right)}}{\partial\sigma} = {\frac{1}{\sqrt{2\pi}}\left( {1 - \frac{X_{0}}{\sigma}} \right)\left( {1 + \frac{X_{0}}{\sigma}} \right){\exp \left( {{- \frac{1}{2\sigma^{2}}}X_{0}^{2}} \right)}}} & (7)\end{matrix}$

[0214] The maximum illumination f(x0) on the outermost circumference(edge) of the detection area 4 in the direction of the x axiscorresponding to the photo-sensitive surfaces of the TDI image sensors205 a and 206 a is about 60.7% of the luminance f(0) at the center ofthe detection area 4. This is because equating the expression on theright-hand side of Eq. (7) to 0 yields x0=σ (for σ=1, x0=1) andsubstituting σ for x0 in Eq. (6) results in the maximum valuef(x0)=0.607f(0). It should be noted that, for x0=0.8σ to 1.2% in Eq.(6), f(x0)=0.49f(0) to 0.73f(0). In this case, for σ=1, x0=0.8 to 1.2(for the Gaussian beam 1007, a reshaping error in the range ±20% causedby the illumination optical system comprising the components 102 to 104is allowable). For σ=0.8×0 to 1.2×0 in Eq. (6) which means that, forx0=1, σ=0.8 to 1.2 (for the Gaussian beam 1007, a reshaping error in therange ±20% caused by the illumination optical system comprising thecomponents 102 to 104 is allowable), f(x0)=0.46f(0) to 0.71f(0). Thus,if a reshaping error of the Gaussian beam 1007 in the range ±20% causedby the illumination optical system comprising the components 102 to 104is allowable for x0=σ (for σ=1, x0=1), the ratio of the illuminationf(x0) on the outermost circumference (the periphery) of the detectionarea 4 to the illumination f(0) at the center (the optical axis 2001) ofthe detection area 4 is in the range 0.46 to 0.73, or f(x0)=0.46f(0) to0.73f(0). It should be noted that, if a reshaping error of the Gaussianbeam 1007 in the range ±10% caused by the illumination optical systemcomprising the components 102 to 104 is allowable for x0=σ (for σ=1,x0=1), the ratio of the illumination f(x0) on the outermostcircumference (the periphery) of the detection area 4 to theillumination f(0) at the center (the optical axis 2001) of the detectionarea 4 is in the range 0.54 to 0.67, or f(x0)=0.54f(0) to 0.67f(0).

[0215] In either case, by reshaping a Gaussian beam 1007 by means of theillumination optical system comprising the components 102 to 104 so thatthe ratio of the illumination f(x0) on the outermost circumference (theperiphery) of the detection area 4 to the illumination f(0) at thecenter (the optical axis 2001) of the detection area 4 is set at a valuein the range 0.46 to 0.73, the beam emitted by the illumination-lightsource 101 can be utilized effectively to increase the illumination onthe periphery of the detection area 4 to a value close to a maximum.

[0216]FIG. 39 is a diagram showing a graph representing a relationbetween the width of illumination in the direction of the x axis or thestandard deviation σ and the illumination (or the quantity of light perunit area) f(x0=1) on a circumference (x0=1) in the direction of the xaxis in the detection area 4 for a fixed quantity of a light or a fixedtotal illumination of a light emitted by the illumination-light source101.

[0217]FIG. 40 is a diagram showing graphs each representing a relationbetween the coordinate x0 in the direction of the x axis in thedetection area 4 and the illumination (or the quantity of light per unitarea) f(x0) for a fixed quantity of a light or a fixed totalillumination of a light emitted by the illumination-light source 101with the width of illumination or the standard deviation σ taken as aparameter. The figure shows graphs for parameter values of 0.5, 1 and 2.

[0218] As is obvious also from FIGS. 39 and 40, in order to set theillumination on a circumference (x0=1) in the direction of the x axis inthe detection area 4 at a value close to a maximum, the beam is radiatedwith the width σ of the illumination in the direction of the x axisbased on the Gaussian distribution generated by the illumination opticalsystem comprising the components 102 to 104 set at a value of about 1(that is, the standard deviation σ=x0). Let x0 denote the distance fromthe center of the detection area 4 or the optical axis to thecircumference in the direction of the x axis as shown in FIG. 37. Inthis case, if the illumination optical system comprising the components102 to 104 reshapes a light emitted by the illumination-light source 101into a slit-shaped beam 1007 having an illumination of the Gaussiandistribution for a standard distribution σ substantially equal to x0(which is the distance from the center of the detection area 4 or theoptical axis to the circumference in the direction of the x axis asdescribed above) and radiates the beam 1007 to the illumination area 3on the inspected substrate 1, the illumination on a circumference (x0=1)can be maximized. It should be noted that the illumination area 3 is anarea with f equal to at least 0.2×f(0) where the symbol f denotes theillumination on the circumference indicated by Lx and Ly.

[0219] It should be noted that, in actuality, TDI image sensors or2-dimensional linear image sensors are used as the detectors 205 and206. In this case, a pixel with a smallest MTF separated farthest fromthe optical axis 2001 is located at a corner of the detection area 4. Inthe case of a TDI image sensor, pixels with a smallest MTF separatedfarthest from the optical axis 2001 are pixels 205 ac and 206 ac locatedat the corners as shown in FIG. 38. Thus, it is desirable to set x0 atthe square root of ((H/2)²+(W/2)²) where the symbols H and Wrespectively denote the width (the length) in the direction of the xaxis and the width in the direction of the y axis of the detection area4 on the inspected substrate 1. If W can be ignored, x0=(H/2). The widthin the direction of the x axis and the width in the direction of the yaxis of a photo-sensitive area (an image-pickup area) on the TDI imagesensor or the 2-dimensional linear image sensor are thus (H×M) and (W×M)respectively. It should be noted that the symbol M denotes themagnification of the image-formation optical system comprising thecomponents 201 to 204.

[0220] As described above, by setting the coordinate x0 of thecircumference in the direction of the x axis in the detection area 4 (orin the case of a TDI image sensor or a 2-dimensional linear imagesensor, the coordinate x0 of pixels separated farthest from the opticalaxis 2001) at the square root of ((H/2)²+(W/2)²) or (H/2) and by havingthe illumination optical system comprising the components 102 to 104reshape a light emitted by the illumination-light source 101 into aslit-shaped beam 1007 having an illumination of the Gaussiandistribution for a standard distribution σ substantially equal to x0 andradiate the beam 1007 to the illumination area 3 on the inspectedsubstrate 1 where the illumination area 3 is an area with f equal to atleast 0.2×f(0) where the symbol f denotes the illumination on thecircumference indicated by Lx and Ly, high-efficiency illumination canbe implemented by using a low-cost ordinary illumination-light source101 without the need to employ a special illumination-light source witha high power output. Examples of such a low-cost illumination-lightsource 101 are a laser-beam source such as a semiconductor laser, anargon laser, a YAG-SHG laser or an exima laser and a filament lightsource such as a xenon lamp, an electric-discharge tube such as mercurylamp and a halogen lamp. As a result, the detection optical systemcomprising the components 201 to 204 is capable of increasing theintensity of a scattered light or a diffraction light generated by adefect such as an infinitesimal foreign particle receiving a lightradiated to pixels on the peripheries of the detectors 205 and 206 witha lowest MTF. Thus, a defect such as an infinitesimal foreign particlewith a size in the range around 0.1 to 0.5 μm or even an infinitesimalforeign particle with a size smaller than about 0.1 μm can be detectedwith a high degree of sensitivity and at a high speed (or at a highthroughput). It should be noted that, even though the illumination in anarea in the direction of the x axis varies in dependence on thecoordinate x0 as indicated by f(x0)=0.46×f(0) to 0.73×f(0), theinspection object 1 is moved in the direction of the y axis so that theimage-signal processing unit 400 compares an image signal with anotherimage signal obtained from the same pixel array in the direction of thex axis in the detection area 4 detected by the detectors 205 and 206which are each implemented typically by a TDI image sensor. Thus, thereis substantially no effect of the difference in illumination between thecenter and the periphery. Then, the image-signal processing unit 400extracts a difference in image signal between chips or cells which arerepeated in the same circuit pattern on the basis of image signalsdetected by the detectors 205 and 206 each implemented typically by aTDI image sensor while the inspection object 1 is being moved in thedirection of the y axis. By comparing the extracted difference in imagesignal using a desired criterion, a defect such as a foreign particlecan be detected during the inspection.

[0221] In this case, the fact that the illumination (or the quantity oflight) on the periphery of the detection area 4 is increased to a valueclose to a maximum is important. In this embodiment, the illumination onthe periphery of the detection area 4 is increased to a value close to amaximum by changing the width of the illumination by means of theillumination optical system comprising the components 102 to 104. As analternative, the illumination on the periphery of the detection area 4is increased to a value close to a maximum by changing the shape of asecondary light source of the illumination by means of the illuminationoptical system comprising the components 102 to 104. As anotheralternative, the illumination on the periphery of the detection area 4is increased to a value close to a maximum by varying the size at thelocation of a Fourier transformation for forming the secondary lightsource.

[0222] In addition, since a DUV (deep ultraviolet) laser source isemployed as the illumination-light source 101, it is necessary to useimage sensors 205 and 206 that are sensitive to a DUV laser. Ifsurface-radiation TDI image sensors shown in FIG. 41(a) are employed asthe image sensors 205 and 206, however, an incident light passes througha cover glass 805, gates 801 between metallic films 802 and an oxidefilm (SiO₂ film) 803 before hitting CCDs created on an Si substrate 804.Thus, since an incident light having a small wavelength is attenuated,the sensor becomes substantially insensitive to a light with awavelength of 400 nm or smaller. As a result, the DUV light may not bedetected. In order to make the surface-radiation TDI image sensorsensitive to a DUV light, there is provided a technique whereby thethickness of the oxide film 803 beneath the gates 801 is reduced so thatthe amount of attenuation of a light with a small wavelength isdecreased. As another technique, the cover glass 805 is coated with anorganic thin film. With such an organic thin film, a visible light isemitted in accordance with an incident DUV light. In this way, the DUVlight is detected as a visible light by a sensor that is sensitive onlyto the visible light.

[0223] On the other hand, the thickness of the Si substrate 804 isreduced as shown in FIG. 41(b) to provide back-surface-radiation TDIimage sensors which each receive an incident light hitting the thin Sisubstrate 804 on the rear side as the image sensors 205 and 206. Sincean incident light hits the surface on the rear side including no gatestructure, the DVD quantization efficiency is increased by about 10% ormore to give a high quantization efficiency and a large dynamic range.As a result, the sensor becomes sensitive to a light having a wavelengthof 400 nm or smaller. In addition, by having the image sensors 205 and206 go TDI (Time Delay Integration) as described above, the sensitivitycan be improved.

[0224] As described above, according to the fourth embodiment, byincreasing the illumination on the periphery of the detection area 4detected by the detectors 205 and 206 each implemented by typically aTDI image sensor to compensate for a decrease in MTF which becomessmaller as the detected position is separated away from the optical axis2001 in the detection optical system comprising the components 201 to204, the illumination efficiency can be increased. As a result, byemploying a low-cost light source such as laser source, it is possibleto detect a defect such as an infinitesimal foreign particle with a sizein the range around 0.1 to 0.5 μm or even an infinitesimal foreignparticle with a size smaller than about 0.1 μm on an inspected substratesuch as an LSI wafer with a high degree of sensitivity and at a highthroughput.

[0225] In addition, according to the fourth embodiment, an optical imagebased on a UVD (deep ultraviolet) laser light such as an exima laserlight obtained from a substrate being inspected is made receivable by aTDI image sensor so that a defect such as an infinitesimal foreignparticle with a size in the range around 0.1 to 0.5 μm or even aninfinitesimal foreign particle with a size smaller than about 0.1 μm onthe substrate being inspected can be detected.

[0226] The following description explains the image-signal processingunit 400 common to the first to fourth embodiments of the presentinvention described above.

[0227] There are variations in detection signal received from thedetectors 205 and 206. Such variations are caused by subtle differencesin process for fabricating the device such as an LSI on the actualsubstrate 1 being inspected and caused by noise generated during thedetection. For example, a signal level 73 for a pixel corresponding to achip 71 is different from a signal level 74 for a pixel corresponding toa chip 72 as shown in FIG. 27(a), resulting in a variation. To put itconcretely, variations in detection signal for locations 75, 76 and 77with pattern structures different from each other are also differentfrom each other as shown in FIG. 27(b). Examples of the locations 75, 76and 77 with pattern structures different from each other are amemory-cell area, a peripheral-circuit area and an area of another typein the case of a memory LSI. As a result, in a portion with smallvariations, it is possible to detect a small defect generatingrelatively small signal changes. In a portion with big variations, onthe other hand, it is possible to detect only a large defect generatingrelatively big signal changes.

[0228] In order to solve the problem described above, the presentinvention provides an image-signal processing unit 400 characterized inthat a variation (a standard deviation) among chips is computed for eachpixel in the chip and used for setting a threshold value, and a defectsuch as a foreign particle in an area with a small variation is detectedby using a small threshold value while a defect such as a foreignparticle in an area with a big variation is detected by using a largethreshold value. In this way, the threshold value for an area with asmall variation can be reduced without being affected by an area with abig variation. An example of an area with a small variation is thememory-cell area in the case of a memory LSI. As a result, it ispossible to detect an infinitesimal foreign particle with a size notexceeding 0.1 μm.

[0229]FIG. 28 is a diagram showing a first embodiment implementing theimage-signal processing unit 400. As shown in the figure, the firstembodiment implementing the image-signal processing unit 400 comprises:an A/D converter 401 for converting an analog image signal into digitaldata wherein the analog image signal represents concentration valuesaccumulated for each array of pixels and is obtained synchronously witha movement of the inspected substrate 1 in the direction of the y axisfrom the image sensors 205 and 206 each implemented typically by a TDIimage sensor; a start/stop command circuit 416 for establishing samplingtiming; a data memory 404; a maximum/minimum removing circuit 405 forremoving signals with maximum and minimum levels; a square computingcircuit 406 for computing the square of a signal level s; a signal-levelcomputing circuit 407 for computing the signal level s; a samplecounting circuit 408; a square integrating circuit 409 for integratingsquares of the signal level s; a signal-level integrating circuit 410for integrating values of the signal level s; a sample-count computingcircuit 411 for computing a sample count n by integration; apositive-threshold-value computing circuit (an upper-criterion computingcircuit) 412; a negative-threshold-value computing circuit (alower-criterion computing circuit) 413; a comparison circuit 414 foroutputting a signal used for indicating a defect such as a foreignparticle and obtained as a result of comparison of a detection signaltemporarily stored in the data memory 404 with a positive thresholdvalue computed and set by the positive-threshold-value computing circuit412; a comparison circuit 415 for outputting a signal used forindicating a defect such as a foreign particle and obtained as a resultof comparison of a detection signal temporarily stored in the datamemory 404 with a negative threshold value computed and set by thenegative-threshold-value computing circuit 413; and a detection-resultoutput means 417 for outputting a result of detection comprising: thesignals received from the comparison circuits 414 and 415 to indicate adefect such as a foreign particle; positional coordinates in acoordinate system established for the inspected substrate 1; andinformation on the inspected substrate 1. It should be noted that themaximum/minimum removing circuit 405 is not necessarily required. If themaximum/minimum removing circuit 405 is not employed, all detectedpieces of image data including image data indicating a foreign particleare used in the computation of the threshold values so that thethreshold values can be calculated with a high degree of accuracy and ahigh degree of stability. By using the computed threshold value, on theother hand, it is impossible to detect a foreign particle in an area forwhich the threshold value is computed. It is thus necessary to compute athreshold value for an area to be inspected from signals generated by anarea corresponding to another chip array on the inspected substrate 1.In consequence, since a line for computing a threshold value isdifferent from a line for inspection, the throughput of the inspectionis reduced to a certain degree. Particularly, in the case of a low chipcount, a threshold value can be computed by using image data spread overa plurality of lines. In this case, a data fetch position is specifiedby the start/stop command circuit 416.

[0230] The detection-result output means 417 is provided with a CPU forcontrolling the whole defect inspecting apparatus provided by thepresent invention for detecting a defect such as a foreign particle. Thecomponents 406 to 411 are used for finding a variation σ of a backgroundsignal for each predetermined area in a chip. The variation σ of abackground signal for each predetermined area in a chip is then used bythe positive-threshold-value computing circuit 412 and thenegative-threshold-value computing circuit 413 to set a positivethreshold value TH(H) and a negative threshold value TH(L) respectivelywhich each serve as a criterion for extracting a signal indicating adefect such as a foreign particle. The components 406 to 413 constitutea threshold-value setting circuit 424. On the other hand, the datamemory 404 is used for temporarily storing detected digital imagesignals till threshold values are set by the threshold-value settingcircuit 424. Positional coordinates in a coordinate system establishedfor the inspected substrate 1 are found on the basis of displacements ofthe stages measured by a measurement apparatus not shown in the figureand read signals (scanning signals) output by components such TDI imagesensors with a reference mark on the inspected substrate 1 used as anorigin. Reference numeral 421 denotes another output means fordisplaying the positive threshold value Th(H) showing a variation (astandard deviation σ) typically on a display means. By providing thedisplay means 421, it is possible to form a judgment as to whether ornot a threshold value is correct for each area in a chip while watchingan output for a defect such as a foreign particle extracted from thecomparison circuits 414 and 415.

[0231] The detection-result output means 417 may include a display meanssuch as a CRT, a printing means for printing detection results as a hardcopy, a recording means such as a hard disc, a floppy disc, anphoto-magnetic recording medium, an optical recording medium, an LSImemory or an LSI memory card and a network connected to anotherinspection apparatus, an inspection system or a control system forcontrolling fabrication process equipment or fabrication lines. Inaddition, as described above, the detection-result output means 417 isprovided with a CPU for controlling the whole defect inspectingapparatus provided by the present invention for detecting a defect suchas a foreign particle.

[0232] The A/D converter 401 converts signals output by the detectors205 and 206 each implemented typically a TDI image sensor into a digitalsignal representing a pixel signal. The A/D converter 401 can be placedon the same substrate as the detection signal processing system 400 orat a location in close proximity to the detectors 205 and 206 eachimplemented typically a TDI image sensor in the detection optical system200. If the A/D converter 401 is at a location in close proximity to thedetectors 205 and 206, the effect of noise is reduced due todigitization upon transmission but, on the other hand, there is ademerit of an increased number of signal transmission cables.

[0233] The following description explains signal processing carried outby the threshold-value setting circuit 424 with reference to FIG. 27.FIG. 27(a) is a diagram showing a typical layout of chips 71 and 72 andother devices on the wafer 1. In most of LSI fabrications, the samechips are created on the wafer repetitively. In some cases, a pluralityof chips, for example, 2 to 4 chips, are created at the same time at aone-time exposure. Thus, at the locations of the chips, the samepatterns are created. As a result, detection signals generated at thepositions of the chips are naturally identical with each other.

[0234] Let notation s (i, j, f, g) denote a signal of a pixel (i, j) ina chip (f, g). As described above, a signal level of a pixel in a chipshould match a signal level of the corresponding pixel in another chip.

[0235] In actuality, however, there are variations in pixel detectionsignal s among chips which are caused by subtle differences amongprocesses but do not indicate a defect, and noise observed in thedetection. In addition, even in the same chip, the variation at alocation with a pattern structure is different from the variation atanother location with another pattern structure.

[0236] The threshold values Th(H) and Th(L) are found from the variation(or the standard deviation σ(s, f, g)) of the detection signal s(i, j,f, g) between a location in a chip and a corresponding location inanother chip in accordance with Eq. (8) as follows:

Th(H)=μ(s, f, g)+m1×σ(s(i, j, f, g), f, g)

Th(L)=μ(s, f, g)−m1×σ(s(i, j, f, g), f, g)  (8)

[0237] where notations Th(H) and Th(L) denote the positive and negativethreshold values set by the positive-threshold-value computing circuit412 and the negative-threshold-value computing circuit 413 respectivelywhereas notation μ(s, f, g) denotes the average of the values of thesignal for different values of f and g. The average is computed by usingEq. (9) as follows:

μ(s, f, g)=(Σs)/n  (9)

[0238] where Σs(i, j, f, g) is computed by the signal-level computingcircuit 407 for computing the signal level s and the signal-levelintegrating circuit 410 for integrating the signal level s whereas n iscomputed by the sample counting circuit 408 and the sample-countcomputing circuit 411.

[0239] Computed in accordance with Eq. (10) below, σ(s, f, g) is astandard deviation of the signal s for different values of f and g. mldenotes a multiplier (coefficient).

σ(s, f, g)={square root}{square root over ( )}(Σs ² /n−Σs/n)  (10)

[0240] where Σs(i, j, f, g)² is computed by the square computing circuit406 for computing the square of a signal level s and the squareintegrating circuit 409 for integrating the square of the signal levels.

[0241] As described above, the threshold values are found by using avalue obtained as a result of multiplication of the standard deviationσ(s, f, g) by a multiplier ml. Normally, it is considered to bedesirable to set the value of the multiplier m1 at about 6. This isbecause the probability of generation of a value of at least 6σ is about1×10⁻¹¹. At this probability, the number of pixels detected from a waferwith a diameter of 300 mm for pixel dimensions of 2×2 μm is 7×10¹⁰.Thus, the value 6 of the multiplier m1 is found from the fact that areason the entire surface of the wafer generating detection signalsexceeding the threshold values (or the so-called false information) arestatistically smaller in size than 1 pixel. Of course, the value of themultiplier m1 does not have to be set at 6. In other words, it isneedless to say that another value can be selected in order to displaythe effect of the present invention. Also from the fact that the numberof pieces of false information does not have to be smaller than 1, it isquite within the bounds of possibility that another value of themultiplier m1 can be selected.

[0242]FIG. 4 is a diagram showing a second embodiment implementing theimage-signal processing unit 400. The second embodiment is differentfrom the first embodiment in that an image signal of 1 chip is delayedby the data memory 402 and a difference processing circuit 403 extractsa difference in image signal between chips Δs={s(i, j, f, g)−s(i, j,f+1, g)}. Thus, the comparison circuits 414 and 415 extract signals eachindicating a defect such as a foreign particle as a result of comparisonof this differential signal Δs={s(i, j, f, g)−s(i, j, f+1, g)} with theupper threshold value Th(H) and the lower threshold value Th(L)expressed by Eq. (11) below.

[0243] Thus, the threshold-value setting circuit comprising thecomponents 406 to 413 sets the upper threshold value Th(H) and the lowerthreshold value Th(L) based on Eq. (11) as follows:

Th(H)=+m1×σ(s(i, j, f, g)−s(i, j, f+1, g), f, g)

Th(L)=−m1×σ(s(i, j, f, g)−s(i, j, f+1, g), f, g)  (11)

[0244] It should be noted that the standard deviation σ(Δs, f, g) of thedifferential image between adjacent chips is computed by using Eq. (12)as follows.

σ(Δs, f, g)={square root}{square root over ( )}(ΣΔs ² /n−ΣΔs/n)  (12)

[0245] where ΣΔs is computed by the signal-level computing circuit 407for computing the signal level Δs and the signal-level integratingcircuit 410 for integrating the signal level Δs whereas n is computed bythe sample counting circuit 408 and the sample-count computing circuit411. ΣΔs² is computed by the square computing circuit 406 for computingthe square of a signal level Δs and the square integrating circuit 409for integrating the square of the signal level Δs.

[0246] By using the differential image Δs between adjacent chips in thisway, the standard deviation σ is small even if the detected image signalin the chip exhibits distribution. As a result, a defect such as aforeign particle can be detected with a higher degree of sensitivity.

[0247] Assume that the process condition varies stage by stage from areato area starting from the center toward the outermost circumference of awafer. In this case, the signal level also changes stage by stage fromarea to area starting from the center toward the outermost circumferenceof the wafer. As a result, the variation (or the standard deviation σ(s,f, g)) used in the computation of the threshold values based on Eq. (8)increases. However, the difference in signal between only adjacent chips(or the standard deviation σ(Δs, f, g)) is actually not so large as thatused in Eq. (8), making it possible to detect a defect by usingthreshold values which are smaller. Thus, the computations using Eqs.(11) and (12) which are based on the differential value Δs allowthreshold values of lower levels to be resulted in.

[0248] As an improved technique, threshold values can also be computedby using Eq. (13) as follows.

Th=m1×σ(|s(i, j, f, g)−s(i, j, f+1, g)|, f, g)  (13)

[0249] where notation |Δs| denotes the absolute value of thedifferential signal Δs.

[0250] In order to compute threshold values by using Eq. (13), thedifference processing circuit 403 is replaced by an absolute-differenceprocessing circuit 403′ to provide image-signal processing units 400shown in FIGS. 29 and 30. A threshold-value computing circuit 423computes a threshold absolute value Th and a comparison circuit 414compares the absolute value of a differential signal with the thresholdvalue Th to extract a signal indicating a defect such as a foreignparticle.

[0251] It should be noted that, in this case, the standard deviationσ(|Δs|, f, g) of a difference in image between adjacent images iscomputed by using Eq. (14) as follows:

σ(|Δs, f, g)={square root}{square root over ( )}(ΣΔs ² /n−Σ|Δs|/n)  (14)

[0252] where Σ|Δs| is computed by the signal-level computing circuit 407for computing the signal level |Δs| and the signal-level integratingcircuit 410 for integrating the signal level |Δs|.

[0253] By the way, in comparison with the third embodiment shown in FIG.29, the fourth embodiment shown in FIG. 30 has an additional memoryposition controller 422. The memory position controller 422 specifiescoordinates of the detection signal s or the differential signal Δs onthe wafer. That is to say, coordinates of pixels on the wafer, for whicha standard deviation σ between chips is found, can be specifiedarbitrarily. In addition, since coordinates on the wafer can bespecified arbitrarily, a standard deviation σ can also be found fromareas surrounding target pixels on chips.

[0254] In the case of the third embodiment shown in FIG. 29, positionalcoordinates on the wafer are found from a result of counting the numberof signals. This technique of finding positional coordinates is good fora case in which a standard deviation a is found from chips laid out on ahorizontal array. However, this technique can not be used to find astandard deviation σ from chips on different arrays.

[0255] In order to solve this problem, the memory position controller422 computes positional coordinates of an incoming detection signal s oran incoming differential signal Δs from signals of the stage coordinatesystem and the like which are obtained from the stage controller 305 asis the case with the third embodiment. The computed positionalcoordinates are then supplied to the square integrating circuit 409, thesignal-level integrating circuit 410 and the sample-count computingcircuit 411 which each have a memory function. In this way, dataproduced by the square integrating circuit 409, the signal-levelintegrating circuit 410 and the sample-count computing circuit 411 canbe stored in the storage destination, that is, at the coordinates of thedetection signal With such a configuration, the number of samples forcomputing a standard deviation can be increased even in the case of awafer periphery at which the number of chips on an array is small. As aresult, the threshold-value computing circuit 423 is capable ofcomputing stable threshold values.

[0256] By letting the absolute-difference processing circuit 403 computethe absolute value of a difference as described above, there isexhibited an effect of, among others, a reduced storage size of the datamemory 404 since data to be stored therein does not have a sign. Inaddition, from a result of computation of an absolute value, acalculated standard deviation σ can be made smaller than a calculationresult obtained from a differential value. In order to obtain ageneration probability of 1×10⁻¹¹, or to get a ‘6σ’ on the normaldistribution, a magnification of about 10 which is about 1.66 times ‘6’is required. That is to say, it can be considered that a calculatedstandard deviation σ can be reduced to a value equal to 0.6 times acalculation result obtained from a differential value.

[0257] In addition, with this technique, a threshold value for a signallevel s is not left, raising a problem in process control and failureanalyses. In order to solve this problem, there is provided a circuit418 for computing the level of a threshold value for a position (i, j)in a chip as a threshold-value map as shown in FIGS. 29 and 30. In thiscircuit 418, a threshold-value map is computed from a sum (σ×m1+Σ|Δs|/n)in which the product σ×ml is calculated by the threshold-value computingcircuit 423 in accordance with Eq. (14) where the symbol σ denotes astandard deviation and the symbol ml denotes a multiplier, and theaverage Σ|Δs|/n of the absolute values of differential signals iscomputed by the average-value computing circuit 425. The result of thecomputation by the circuit 418 for each positional data (i, j) computedfrom the positions of the stages 301 and 302 as well as the sensors 205and 206 is stored in a threshold-value-map storage means 419 which has amemory for each pixel (i, j) on the entire chip. The threshold-value mapcan be displayed on a threshold-value map output means such as a displaymeans 421 as requested by the user. In addition, a threshold-value mapand outputs each indicating a defect such as a foreign particleextracted from the comparison circuit 414 are also displayed on thedisplay means 421, allowing the user to form a judgment as to whether ornot the threshold values are proper. Furthermore, by supplyinginformation of the threshold-value map to the detection-result outputmeans 417, it is possible to output a threshold-value map and pieces ofdata each indicating a defect such as a foreign particle extracted fromthe comparison circuit 414.

[0258] Related to the condition of an underlying layer, thethreshold-value level corresponds to information indicating whether ornot the underlying layer is a repetitive-pattern area, an area includinga terribly poor spot, a thin-film area or an area with small patterndimensions. It is thus important to analyze which threshold-value levela detected foreign particle has been detected with respect to.Therefore, it will be meaningful to output a threshold value at aposition of a detected foreign particle as data of the detected foreignparticle added to the signal level of the foreign particle by displayingthe threshold value on the display means 421. For this reason, thecomputed threshold-value map is required.

[0259] By the way, instead of the signal level s of a foreign particlewhich is ‘a differential value+a threshold value’, it can be consideredto be the use of the differential value Δs.

[0260] In addition, as underlying data at the position of a detectedforeign particle, information derived from design data can also be usedin addition to the threshold-value level described above. Examples ofsuch information are information on an area in a chip such as a memoryarea, a logic-circuit area, a power-supply area and a wireless area. Inorder to make such information available, a map of areas in a chip ismade from the design data, then an information or a phrase being similarto threshold-value data which is coded from coordinates of the made areamap may be output by being displayed in an operation to display adetected foreign particle.

[0261] Furthermore, it is possible to output by displaying underlyingarea data of any of the types described above, in the form of a foreignparticle map for each type of underlying data or in the form of aforeign particle count for each type of underlying data.

[0262] As described above, according to the basic concept of the presentinvention, the magnitude of the variation of a signal is found and athreshold value is determined in accordance with the found magnitude ofthe variation of the signal. In a typical configuration of the presentinvention, the threshold-value setting circuit 424 computes a thresholdvalue for each of corresponding pixels in chips from data of the chipsacquired in advance. Threshold values are computed in advance for thesame processes of LSIs of the same type. The computed threshold valuesare typically stored in a threshold-value memory employed in thethreshold-value setting circuit 424 to be compared by the comparisoncircuits 414 and 415 with sequentially incoming signal levels. Data usedin the computation of threshold values can be found once for a lot whichnormally comprises 13 to 25 wafers or found for each wafer.

[0263] It should be noted that, in the present invention, since athreshold-value level varies in dependence on the condition of anunderlying layer as described above, the threshold-value levelrepresents the condition of the underlying layer. That is to say, theCPU as an output means 417 is capable of knowing what underlying layer adefect such as a foreign particle exists on or is attached to, providedthat signals each indicating a defect such as a foreign particle areclassified by threshold-value levels obtained from thethreshold-value-map storage means 419. The condition of an underlyinglayer, for example, indicates that the underlying layer is an area withno pattern, an area of cells or an area of peripheral patterns. As analternative, the CPU 417 can be inputted CAD information from a CADsystem by way of an input means 426 which is typically implemented by anetwork or storage media. In this case, the CPU 417 produces area datain a chip like the ones shown in FIGS. 1 and 2 on basis of the inputtedCAD information and is capable of further knowing directly the conditionof an underlying layer being existed a defect such as a foreign particleby using the area data in a chip.

[0264] The technique of inferring the condition of an underlying layerfrom a signal level or a threshold-value level of the underlying layerwithout using area data exhibits an effect that it is not necessary toset areas in a chip in advance. In this case, the CPU 417 is capable ofclassifying signal levels of the underlying layer as areas such as cellunits from the magnitudes of threshold-value levels of the entire chipfound once from a threshold-value map stored in threshold-value-mapstorage means 419. In this case, a judgment for an area can be formed bycomparing the threshold-value level with a difference As in signal levelbetween adjacent chips or the signal level itself. After knowing thecondition of the underlying layer, the CPU 417 is capable of detecting,outputting and controlling a defect or a foreign particle only, forexample, on a cell unit.

[0265] Next, a fifth embodiment implementing the central processing unit400 is explained by referring to FIG. 31. The fifth embodiment computesa difference Δs in detection signals (or data) between adjacent chipsand then finds a variation (or a standard deviation σ(Δs, f, g)) of datasurrounding a target pixel.

[0266] The fifth embodiment includes delay memories 425 and 426 and awindow opening circuit 427 to form the so-called pipeline processingsystem. Components 406 to 413 compute the variation σ(Δs, f, g) fromperiphery pixels' differential values Δs(i+1, j+1, f, g), Δs(i+1, j, f,g), Δs(i+1, j−1, f, g), Δs(i, j−1, f, g), Δs(i−1, j−1, f, g), Δs(i−1, j,f, g), Δs(i−1, j+1, f, g) and Δs(i, j+1, f, g) of a window excluding acentral differential value Δs(i, j, f, g) of the window in accordancewith Eq. (15) given below. Then, the threshold values Th(H) and Th(L)are computed in the basis of the computed standard deviation σ.

σ(Δs, f, g)={square root}{square root over ( )}(ΣΔs^(2/)8−Σs/8)  (15)

[0267] The comparison means 414 and 415 compare the central differentialvalue Δs(i, j, f, g) of the window cited above with the computedthreshold values Th(H) and Th(L) respectively to extract a defect suchas a foreign particle. The dimensions of the window do not have to be3×3 as shown in the figure. Instead, they can be 4×4, 5×5 or 7×7. As analternative, the computation can be applied to a plurality of windowsizes. In addition, the object of inspection is not necessarily thecentral differential value. Instead, the object of inspection can be anydifferential value in the window. As another alternative, the object ofinspection can be another value such as an average or a sum ofdifferential values of a plurality of pixels on the window. The size ofthe window should be determined in accordance with the size of a foreignparticle to be detected or the shape of a background pattern.

[0268] The following description explains a sixth embodimentimplementing the central processing unit 400 wherein a threshold valueof the absolute sensitivity is set. By setting a threshold value of theabsolute sensitivity based on Eq. (13) given above, the control size ofa foreign particle or a defeat in LSI fabrication processes can be madeuniform for all the processes.

[0269] The CPU 417 of the detection signal processing circuit 400corrects a signal level or preferably a differential signal level sswhich is received as a result of detection in addition to coordinates ofa foreign particle.

[0270] To put it concretely, the differential signal level ss iscorrected into a differential signal level ss′ in accordance with Eq.(16) as follows:

ss′=ss/(P1×ND×k×rb×k(t))  (16)

[0271] where the symbol P1 denotes the power of a laser generated duringinspection, the symbol ND denotes the ND of the ND filter expressed interms of %, the symbol k denotes a constant indicating whether or not apolarization plane exists, the symbol rb denotes the reflectance of theunderlying layer and the symbol k(t) denotes a correction coefficientdependent on the thickness t of the oxide film. A value of 1 of theconstant k indicates that a polarization plane exists while the constantk is desirably set at around 10 to indicate that a polarization planedoes not exist. It should be noted that, since the laser power P1exhibits a distribution characteristic P1(x) known as the so-calledshading over illumination positions along the x axis, the value of P1(x)can be substituted for P1 in Eq. (16) to give a better result.

[0272] The size d of a foreign particle or a defect is a function df(ss)of differential signal level ss obtained in advance. In actuality, thesize d of a foreign particle or a defect displayed on the display means421 is found by substituting the corrected differential signal level ss'for the differential signal level ss in the function df(ss) as follows:

d=df(ss′)  (17)

[0273] In particular, for a small foreign particle, according to Mie'sscattering theory, the corrected differential signal level ss′ isproportional to the (−6)th power of the size d of the foreign particle.Thus, the size d of the foreign particle can also be found from thisproportional relation.

[0274] The following description explains an embodiment implementing thecentral processing unit 400 wherein a judgment on the existence of adefect is based on a high S/N ratio for of course an infinitesimalforeign particle and a large foreign particle having a spreading shape.By the way, it is necessary not only to detect an infinitesimal foreignparticle but also not to miss a large foreign particle or a foreignparticle having a thin-film shape spread over a range of several micronsby using the comparison circuits 414 and 415 employed in the centralprocessing unit 400 for forming a judgment on the existence of a defect.Since a high-level detection signal is not always generated by such alarge foreign particle, however, the S/N ratio of a detection signal ofa pixel unit is low, causing such a large foreign particle to beneglected.

[0275] Let the symbol S denotes an average detection signal level of 1pixel and notation σ/n denotes an average variation. By convolution foran extracted unit having dimensions of n pixels×n pixels whichcorrespond to the size of a large foreign particle, the level of thedetection signal is found to be n²S, the variation is found to be nσ andthe S/N ratio is found to be nS/σ. If a large foreign particle isdetected in pixel units, on the other hand, the level of the detectionsignal is found to be S, the variation is found to be σ and the S/Nratio is found to be S/σ. Thus, by convolution for an extracted unithaving dimensions of n pixels×n pixels which correspond to the size of alarge foreign particle, the S/N ratio is increased by n times.

[0276] As for an infinitesimal foreign particle with a size of about 1pixel, the level of a detection signal detected for a 1-pixel unit isfound to be S, the variation is found to be σ and the S/N ratio is foundto be S/σ. By convolution for an extracted unit having dimensions of npixels×n pixels in the case of an infinitesimal foreign particle with asize of about 1 pixel, on the other hand, the level of the detectionsignal is found to be S/n², the variation is found to be nσ and the S/Nratio is found to be S/nσ. Thus, for an infinitesimal foreign particlewith a size of about 1 pixel, by keeping the signal of a pixel unit asit is, the S/N ratio can be increased.

[0277] It is thus obvious from the description given above that, byconvolution of an image signal obtained from the data memory 404 foreach extracted operator 520, a gray scale image signal with differentlevels is output from pixels at the center. There are a plurality ofoperators 520 with different dimensions expressed in terms of pixelunits for detection of a defect. As shown in FIG. 52, examples of theoperators 520 are an operator 521 extracted as 1 pixel unit, an operator522 extracted as a unit of 3 pixels×3 pixels, an operator 523 extractedas a unit of 4 pixels×4 pixels, an operator 524 extracted as a unit of 5pixels×5 pixels and an operator 525 extracted as a unit of n pixels×npixels. In this case, the levels of the gray scale image signal are S,9S, 16S, 25S and n²S for the operators 521, 522, 523, 524 and 525respectively where the symbol S denotes an average detection signallevel of 1 pixel. On the other hand, multiplication circuits 541, 542,543 and 544 multiply a threshold value m1×σ output by a threshold-valuecircuit 423 employed in the threshold-value setting circuit 424 byapproximation threshold-value coefficients 3, 4, 5 and n respectively.These approximation threshold-value coefficients 3, 4, 5 and n areinferred from the central limit theorem. Comparison circuits 531, 532,533, 534 and 535 constitute a comparator 414′. In the comparison circuit531, the gray scale image signal obtained as a result of the convolutionat the operator 521 is compared with the threshold value m1×σ in orderto form a judgment on the existence of a defect such as a foreignparticle and to output a signal indicating a foreign particle inaccordance with the outcome of the judgment. In the comparison circuit532, on the other hand, the gray scale image signal obtained as a resultof the convolution at the operator 522 is compared with a thresholdvalue obtained as a product of the threshold value m1×σ and theapproximation threshold-value coefficient 3 in order to form a judgmenton the existence of a defect such as a foreign particle and to output asignal indicating a foreign particle in accordance with the outcome ofthe judgment. Likewise, in the comparison circuit 533, the gray scaleimage signal obtained as a result of the convolution at the operator 523is compared with a threshold value obtained as a product of thethreshold value m1×σ and the approximation threshold-value coefficient 4in order to form a judgment on the existence of a defect such as aforeign particle and to output a signal indicating a foreign particle inaccordance with the outcome of the judgment. Similarly, in thecomparison circuit 534, the gray scale image signal obtained as a resultof the convolution at the operator 524 is compared with a thresholdvalue obtained as a product of the threshold value m1×σ and theapproximation threshold-value coefficient 5 in order to form a judgmenton the existence of a defect such as a foreign particle and to output asignal indicating a foreign particle in accordance with the outcome ofthe judgment. Similarly, in the comparison circuit 535, the gray scaleimage signal obtained as a result of the convolution at the operator 525is compared with a threshold value obtained as a product of thethreshold value m1×σ and the approximation threshold-value coefficient nin order to form a judgment on the existence of a defect such as aforeign particle and to output a signal indicating a foreign particle inaccordance with the outcome of the judgment. That is to say, thecomparison circuit 531 detects an infinitesimal foreign particle with asize of about 1 pixel. On the other hand, the comparison circuit 532detects a foreign particle with dimensions of about 3 pixels×3 pixels.Similarly, the comparison circuit 533 detects a foreign particle withdimensions of about 4 pixels×4 pixels. Likewise, the comparison circuit534 detects a foreign particle with dimensions of about 5 pixels×5pixels. Similarly, the comparison circuit 535 detects a foreign particlewith dimensions of about n pixels×n pixels. A logical-sum circuit 550computes a logical sum of the signals output by the comparison circuits531 to 535 each to indicate a foreign particle. Thus, signals indicatingforeign particles with different dimensions can be detected each at ahigh S/N ratio. As a result, the degree of complementation can be raisedfor a large foreign particle generating a low detection-signal level andhaving a spread shape.

[0278] It should be noted that, by providing operators with differentdimensions expressed in terms of pixels for forming a judgment on theexistence of a defect such as a foreign particle after the differenceprocessing circuit 403′ and a pixel signal is integrated to generate anoutput each time the dimensions expressed in terms of pixels arechanged, the comparator 414 is made capable of detecting a signalindicating a foreign particle with a size matching the changeddimensions expressed in terms of pixels. In this case, however, it isnecessary to carry out the inspection a plurality of times by changingthe dimensions expressed in terms of pixels. Nevertheless, an accuratevalue is set as a threshold value. In addition, if operators withdifferent dimensions expressed in terms of pixels for forming a judgmenton the existence of a defect such as a foreign particle are providedafter the difference processing circuit 403′, an image memory 404 with astorage capacity increased by a plurality of times is required. However,it is not necessary to provide more than one threshold-setting circuit424. In addition, a threshold value m1×σ output by a threshold-valuecircuit 423 employed in the threshold-value setting circuit 424 can bemultiplied by an approximation threshold-value coefficient to find afinal threshold value.

[0279] As described above, by adjusting dimensions expressed in terms ofpixels for formation of a judgment on the existence of a defect such asa foreign particle by integration or convolution of a rectangularfunction to the size of a foreign particle to be detected in thecomparator 414′, it is possible to catch a large foreign particlegenerating a low detection-signal level and having a spread shape.

[0280] The next description explains embodiments implementing atechnique of specifying conditions adopted in the defect inspectingapparatus provided by the present invention for detecting a defect suchas a foreign particle by referring to FIGS. 42 to 46. FIG. 42 is adiagram showing a sequence of specifying conditions followed by thedefect inspecting apparatus provided by the present invention fordetecting a defect such as a foreign particle. Inspection of a substratefor a defect is carried out under conditions set in this sequence.

[0281] As shown in FIG. 42, the sequence begins with a step S41 at whichthe CPU 417 displays a screen for selecting one of a variety of modeslike ones shown in FIG. 43 on the display means 421. By using an inputmeans 426 such as a keyboard or a mouse, the user is allowed to selectan item in each mode. Typical modes include a chip matrix S411 on awafer, a condition specifying mode S412 and a threshold-value advanceselection mode S413. Selectable items of the chip matrix S411 are itemsrelated to chip layout data such as the size of the chip, the startcoordinates of the chip and information indicating non-existence of achip. As shown in FIG. 43, selectable items of the condition specifyingmode S412 are: a. Area priority; b. Standard; c. Sensitivity priority;and d. Post-sensitivity-display selection. On the other hand, selectableitems of the threshold-value advance selection mode S413 are: a. ml 6:False-information generation rate of OO%; b. ml 10: False-informationgeneration rate of OO%; and c. ml 15: False-information generation rateof OO%.

[0282] The ‘a. Area priority’ of the condition specifying mode S411 isan inspection-condition mode which allows a relatively large foreignparticle in an area larger than the standard mode to be detected bytypically weakening the power of the illumination beam. An area with asaturated background level is virtually an uninspectable area. In thearea-priority mode, however, the size of an uninspectable area can bemade 5% or smaller. FIG. 45 is a diagram showing a case in which thearea-priority mode allows a foreign particle having a size of about 2.5μm to be detected from the entire area.

[0283] The ‘b. Standard’ of the condition specifying mode S412 is aninspection-condition mode which allows a foreign particle to be detectedat a standard sensitivity. FIG. 45 is a diagram showing a case in whichthe standard mode allows a foreign particle having a size of about 1.0μm to be detected from about 90% of the entire inspection area andfurthermore to a foreign particle having a size of about 0.2 μm to bedetected.

[0284] The ‘c. Sensitivity priority’ of the condition specifying modeS412 is a mode with the sensitivity set at such a high value that aforeign particle more infinitesimal than that of the standard mode canbe detected, or an inspection-condition mode set to allow a specifieddetection sensitivity to be preserved. FIG. 45 is a diagram showing acase in which the sensitivity-priority mode allows a foreign particlehaving a size of about 0.5 μm to be detected from about 75% of theentire inspection area and furthermore to a foreign particle having asize of 0.1 μm to be detected. To put it concretely, by increasing thepower of the illumination light, the power of the illumination light isset at a level capable of assuring an inspection condition allowing aforeign particle smaller in size than a foreign particle indicated by aspecified detection size or assuring a specified detection sensitivity.In the examples shown in FIG. 45, the inspection condition allows aforeign particle having a size of about 0.1 μm to be detected or thespecified detection sensitivity allows a foreign particle having a sizeof about 0.5 μm to be detected from at least 75% of the inspection area.

[0285] The ‘d. Post-sensitivity-display selection’ of the conditionspecifying mode S412 is a mode displaying results of inspection obtainedin one of the 3 modes described above, or a map of threshold values in achip or a relation between the size (the sensitivity corresponding tothe threshold value) and the inspection area (a threshold-valuehistogram) and allowing the user to select an appropriate item amongwhat are displayed.

[0286] In the area-priority mode, the power of the illumination light islowest and the dynamic range is wide. When the defect inspectingapparatus is switched from the area-priority mode to the standard mode,the power of the illumination light is increased while the dynamic rangeis reduced. The same holds true when the defect inspecting apparatus isswitched from the standard mode to the sensitivity-priority mode. Thus,in the case of the area-priority mode, in the threshold-value map, thereare only few uninspectable areas from which a foreign particle can notbe detected, but only foreign particles with a size of up to about 0.5μm can be detected. In the standard mode, there are many saturateduninspectable areas from which a foreign particle shown in a white colorin FIG. 45 can not be detected. However, foreign particles with a sizeof up to about 0.2 μm can be detected. In the case of thesensitivity-priority mode, there are even more saturated uninspectableareas from which a foreign particle shown in a white color in FIG. 45can not be detected. However, foreign particles with a size of up toabout 0.1 μm can be detected. In the threshold-value histograms,reference numeral 471 denotes a relation between the sensitivity and theinspection area rate, whereas reference numeral 472 denotes a relationbetween the sensitivity and the integration value of the inspectionarea. It should be noted that a threshold-value histogram can also showonly one of the relations 471 and 472.

[0287] An item in the threshold-value advance selection mode S413 can beselected in accordance with an allowable probability of generation offalse information by checking this allowable probability with thedisplayed probabilities of generation of false information (thegeneration frequencies) OO%. This is because, as described earlier,since a threshold value is set from the variation σ of the level of adetected image-picture signal, the probability of generation of falseinformation OO% can be automatically computed for a display from themultiplier ml on the basis of the theory of statistics. Thus, thethreshold value setting and the multiplier m1 for the probability ofgeneration of false information can be displayed with ease.

[0288] The CPU 417 then goes on to the next step S42 of the flow of thesequence shown in FIG. 42. At the step S42, the spatial filter 202 isset either manually or automatically in accordance with the structure ofa circuit pattern on a selected wafer. The CPU 417 then proceeds to astep S43 at which an image formed by the spatial filter 202 is confirmedeither by visual observation or automatically by using an image formedby a TV camera 228 and the image-formation optical system 227, a focusof which is adjusted to the position of the filter as shown in FIG. 46.If the image is not confirmed, the CPU 417 then goes back to the stepS42 to again set the spatial filter 202. If the image is confirmed, onthe other hand, the CPU 417 goes on to the next step. The spatial filter202 has a configuration wherein the pitch and the phase of its opticalshielding pattern can be changed. As shown in FIG. 46, a single assembly225 comprises a beam splitter 204 and a spatial-filter observationoptical system which comprises a half mirror 226, the image-formationlens 227 and the TV camera 228. The internal structure of the assembly225 can be changed as shown by an arrow 230. To be more specific, in anoperation to detect an ordinary foreign particle, the beam splitter 204is placed on the detection optical axis 204. In a spatial-filterobservation, on the other hand, it is the half mirror 226 that is placedon the detection optical axis. In an automatic operation, by subjectinga diffraction light and an optical shielding pattern detected in theaperture 20 a to an image-pickup operation carried out by the TV camera228 in the same way as that shown in FIG. 19(b), the pitch and the phaseof the optical shielding pattern can be adjusted so that the diffractionlight is shield ed. In addition, by shifting the position of the TVcamera 228 in a direction indicated by an arrow 229 in FIG. 46, it isalso possible to adjust the directivity of the optical shielding patternwhile observing also the image of a circuit pattern on the substratebeing inspected.

[0289] Then, the flow of the sequence goes on to a step S44 at which theCPU 417 inputs a value of the magnification (coefficient) m1 in therange around 6 to 15 for the standard deviation σ for setting athreshold value Th from the input means 426. The flow of the sequencethen goes on to a step S45 at which the CPU 417 inputs a detection sizeof a foreign particle from the input means 426 in size specificationS451. The detection size of a foreign particle is used for computing alaser power which can be used to detect a foreign particle having thespecified size. The laser-beam source 101 is then controlled by acontrol signal 430 to generate a laser beam having the computed laserpower.

[0290] Then, the CPU 417 goes on to a step S46 at which, in order to setthreshold values for a partial area or the entire area of a chip, thewafer is scanned and inspected and a threshold-value map computed by thethreshold-value computing means 418 is stored in the threshold-value-mapstorage means 419. Then, the threshold-value map (or a threshold-valueimage) like the one shown in FIG. 44 or threshold-value histograms likethe ones shown in FIG. 45 are displayed on the display means 421. Thehistograms shown in FIG. 45 each represent a relation between thesensitivity and the inspection area having the sensitivity with thesensitivity represented typically by the horizontal axis. Each of thehistograms shown in FIG. 45 also represents a relation between thesensitivity and the integration value of the inspection area. The useris then allowed to check the sensitivity on the basis of typically thedisplayed threshold-value map to confirm whether the threshold value isat a desired level (the size of a foreign particle to be detected). Ifsuch a threshold value is not confirmed, the flow of the sequence goesback to the step S45. If such a threshold value is confirmed, on theother hand, the flow of the sequence goes on to the next step S47.

[0291] As described above, the CPU 417 goes on to the step S47 at whichthe entire area of the wafer is inspected. If an area generating falseinformation exists, such an area may be set as a non-inspection area (aninhibit area) on the basis of CAD information in the chip or informationincluded in the threshold-value map. The flow of the sequence then goeson to a step S48 at which the CPU 417 issues a command to inspect thesubstrate 1 for a defect such as a foreign particle. If the centralprocessing unit 400 determines that a defect such as a foreign particleexists, the level of the detection signal and detection coordinates ofthe defect are stored in a storage unit 427.

[0292] Finally, the flow of the sequence goes on to a step S49 at whichthe actual inspected substrate 1 is optically observed by using anoptical-observation microscope 700 implemented typically by anultraviolet-ray microscope or a common-focus microscope installedbesides the defect inspecting apparatus in order to confirm whether aresult of the inspection indicates a defect such as a foreign particleor is false information. With this confirmation, it is possible toconfirm whether a condition specification has been set properly for thefirst time. In particular, if an area including an infinitesimal andcomplicated circuit pattern coexists with an area causing colornonuniformity in a chip on the inspected substrate 1, it is necessary tofinally confirm the condition specification by using theoptical-observation microscope 700. If the result of the confirmation offalse information done at the step S49 is NO, the flow of the sequencegoes on to a step S50 at which the magnification (coefficient) m1 forsetting a threshold value is increased or decreased in some cases. Theflow of the sequence then goes back to the step S45 at which the laserpower is changed if necessary. In the case of a YES result, on the otherhand, the condition specifying sequence is ended.

[0293] It should be noted that the objective can be achieved even ifonly part of the procedure described above is adopted or if the flow ofthe sequence is changed.

[0294] As described above, it is possible to specify conditions optimumfor a desired size (sensitivity) of a foreign particle with ease andwithin a short period of time.

[0295] It should be noted that, in the optical observation carried outat the step S49, the detected foreign particle (including that falseinformation) on the inspected substrate 1 can be moved to the positionof a detection optical system 701 employed in the optical-observationmicroscope 700 shown in FIG. 46 by moving the stages 301 and 302 so asto allow the inspector to observe the image thereof. In the case of thedetection optical system 200, the image-formation optical subsystemthereof has a high resolution and, in addition, coordinates of a pointof observation are changed during a movement of the object of inspectionwith a high degree of precision. In particular, the dark-visual-fieldillumination optical system comprising the components 102 to 105 allowsa foreign particle with a size smaller than the resolution limit of thedetection optical system 200 to be detected. Thus, with an ordinarymicroscope, observation is impossible in many cases. For this reason,the optical-observation microscope 700 is employed. As theoptical-observation microscope 700, it is desirable to employ typicallya common-focus optical system with an extremely high resolution or anoptical system with a short wave illumination light such as ultravioletrays or deep ultraviolet rays with a typical wavelength of 248 nm, 365nm or 266 nm or a wavelength close thereto. That is to say, for awavelength of about 200 nm, the optical-observation microscope 700 iscapable of producing an image close to an image formed by an electronmicroscope as well as allows the size of a defect such as a foreignparticle to be found with a high degree of precision attributesincluding shapes of defects such as foreign particles to be classified.It should be noted that FIG. 46 shows the configuration of theoptical-observation microscope 700. As shown in FIG. 41, theoptical-observation microscope 700 comprises: the aforementioneddetection optical system 701 having a bright-visual-field ordark-visual-field ultraviolet-ray illumination optical subsystem and aTDI image sensor of FIG. 41 capable of detecting an ultraviolet ray; animage-signal processing unit 702 for carrying out processing such as A/Dconversion of an image detected by the TDI image sensor of the detectionoptical system 701; an image memory 704 for storing an image completingthe A/D conversion in the image-signal processing unit 702 at an addressbased on coordinate data of a foreign particle (or that considered to befalse information) detected by the central processing unit 400; and adisplay means 703 for displaying an image. Thus, by controlling thestages 301 and 302 in accordance with coordinate data of a foreignparticle (or that considered to be false information) detected by thecentral processing unit 400 to display an image considered to be falseinformation on the display means 703 for observation by the inspector,the inspector is capable of confirming the false information by usingthe optical-observation microscope 700. To put it in detail, the stages301 and 302 are moved to take the position indicated by detectioncoordinates stored in the storage unit 427 to the visual field of theoptical-observation microscope 700, and the optical-observationmicroscope 700 detects an image in the visual field and displays on thedisplay means 703 or stores the image in the image memory 704 asnumerical image data. This stored data can be redisplayed whennecessary. In addition, data stored in the image memory 704 can besupplied to the CPU 417 of the central processing unit 400 and observedlater along with image data transferred from another defect inspectingapparatus. Anyway, as the optical-observation optical system 700, abright-visual-field microscope having a high resolution, adark-visual-field microscope having the illumination optical system 100described above, a dark-visual-field microscope having incoherentillumination, a phase-differential microscope or a common-focusmicroscope can be employed.

[0296] In the condition specifying sequence described above, thespecification of conditions can be completed by merely making a chipmatrix at the step S41 and entering the size of a foreign particle to bedetected at the step S45. That is to say, a chip matrix and the size ofa foreign particle (or a sensitivity corresponding to the size of aforeign particle) are conditions that absolutely need to be specified.

[0297] In other words, the confirmation of the filter at the step S43,the setting of the multiplier m1 at the step S44, the confirmation of asensitivity at the step S46, the setting of an inhibit area (anon-inspection area) at the step S47 and the confirmation of falseinformation at the step S49 are optional condition setting steps.

[0298] In addition, in setting of a threshold value, the use of athreshold value on the stable side (a large threshold value) suppressesgeneration of false information. By decreasing the threshold value, onthe other hand, a foreign particle can be detected with a high degree ofsensitivity even if false information is generated to a certain degree.The former technique is suitable for quality control of a waferprocessing apparatus and therefore used for detecting an abnormality.The latter technique is on the other hand suitable for an analysis of astate of generation of a failure and a defect, and thus used forclassifying defects and foreign particles in determining a cause ofgeneration of a failure.

[0299] The following description explains inference of the diameter of aforeign particle carried out by the CPU 417 from a scattered-light imagestored in the image memory 404 as a result of processing comprisingdetection by the image sensors 205 and 206 and A/D conversion by theA/D-conversion unit 401 by referring to FIG. 47. The level of a signalrepresenting a scattered light or, the more desirable differential valuess, varies in accordance with the size of a particle or a defect such asan injury which generates the scattered light. The CPU 417 corrects thedetection signal ss by multiplying the signal ss by a correctioncoefficient k(t) to produce a corrected detection signal ss′. In thiscase, the correction coefficient k(t) is calculated in accordance withconditions including the power of the laser beam, the polarization plane208 on the inspection, the spatial filter 202 and the illuminationangles φ1 and α1 in such a way that the corrected detection signal ss′can be made representative of the size d of an external material or adefect such as an injury. The CPU 417 uses information on the size of aforeign particle or a defect calculated in this way as a size to benormally specified in the detection-size specification at the step S45of the condition specifying sequence described earlier.

[0300] As described earlier, an image representing a foreign particle isdetected by the TDI image sensors 205 a and 206 a and stored in theimage memory 404. A relation between the size of the image (or thenumber of pixels showing the spread of the image of the foreignparticle) and the dimensions of the foreign particle exhibits a certaintrend as shown in FIG. 47. Thus, the CPU 417 is capable of inferring thediameter of the foreign particle by computing the number of pixelsshowing the foreign particle with such pixels obtained from a detectedimage stored in the image memory 404. Particularly, in the case of aforeign particle having a size in the range around 0.13 to 0.2 μm, acorrelation between the size and the dimensions of the image of theforeign particle can be found out. As a result, the size of a foreignparticle or the diameter of a foreign particle can be inferred.

[0301] In addition, in the case of a foreign particle sizeaccommodatable in one pixel and a signal level exceeding the dynamicrange of the image sensors 205 and 206, the size of the foreign particlecan be inferred by using the following technique. Even if the size of aforeign particle can be accommodated in one pixel, an image exhibiting aspread as shown in FIG. 48(a) is formed. From the width between the riseand the fall of this spread, that is, from the width W of the thresholdvalue, the intensity of a signal exceeding a peak level or the dynamicrange can be inferred. In this case, as shown in FIG. 48(b), the surfacecondition of the cover glasses 220 of the image sensors 205 and 206 isset at a specific surface roughness to let the cover glasses 220 causescattering and produce a spreading forcibly. In this way, the size of aforeign particle can be inferred more easily from a detection image.

[0302] Next, a plurality of inspections by the defect inspectingapparatus provided by the present invention are explained. In theinspections, in order to provide a dynamic range, for example, thesurface of the inspected substrate 1 is inspected in the area-prioritymode, the standard mode and the sensitivity-priority mode, that is,under a condition of an increasing power of the illumination light, andin the standard mode or in a condition of a reduced power of theillumination light. Results of the inspections are then supplied to theCPU 417. The results of the inspections can be simply integrated into aninspection-result map. The inspection-result map is a drawing showingplotted defect marks at positional coordinates at which defects such asforeign particles have been detected. The CPU 417 may also produce alist of coordinates of foreign particles or a list/map showingdetection-signal levels of foreign particles in place of such aninspection-result map.

[0303] In addition, a plurality of inspections are carried out not onlyto provide a dynamic range, but carried out also in order to allowdetection of a defect such as an infinitesimal injury or foreignparticle by changing typically the travel times of the stages 301 and302. Furthermore, the inspections are also carried out by changingconditions such as the directions α1, φ1 (including 0) and φ2 (including0) of the illumination set by the illumination optical system 100, thepresence/absence of the polarization plane 208 and the use of thewhite-color illumination 500 and the laser illumination 100.

[0304] In addition, as a technique of processing adopted by the CPU 417,the corrected detection-signal level ss′ of a defect detected under aplurality of inspection conditions is mapped onto a space of multidimensions such as the power of the illumination light, the illuminationdirections, the presence/absence of the polarization plane, thewhite-color illumination and the laser illumination to produceclassified results from a distance in the space with the class portionseparated. For example, as shown in FIG. 49, curves are each plotted toshow a relation between the level ss′ of a detection signal produced bythe laser-illumination optical system 100 on the x axis and the levelss′ of a detection signal produced by another illumination opticalsystem such as the white-color illumination system 500 and theillumination system shown in FIG. 50 on the y axis. The curves areplotted in 2 areas separated by a straight line represented by y=βx setin advance. The classification of the relations into these 2 areasallows a characteristic of a defect to be identified. As describedabove, the illumination system shown in FIG. 50 can be used as anotherillumination system. In this case, results of experiments have verifiedthat a defect such as a foreign particle with a relation thereof plottedin the area represented by y>βx is an injury or a flat foreign particle491 which is not much illuminated by an illumination light in a slantingdirection. On the other hand, a defect such as a foreign particle with arelation thereof plotted in the area represented by y<βx is a foreignparticle 492 with a relatively large height. The boundary line betweenthe 2 areas does not have to be a straight line. That is to say, theboundary line can also be a curve for example. As a matter of fact, aplurality of straight and/or curved lines can serve as boundariesbetween areas. In addition, a space for finding these distances can havea plurality of dimensions. Further, these inspections can be carried outby using the detectors 205 and 206 at the same time.

[0305] Instead of radiating the laser beams 10, 11 and 12 as shown inFIG. 3 in slanting illumination directions, the illumination systemshown in FIG. 50 radiates a laser beam 3 to the inspected substrate 1 ina direction substantially perpendicular to the surface of the substrate1 by reflecting the laser beam 10 using a straight-line-shaped finemirror 240 which is inserted between the objective lens 201 and theinspected substrate 1. Thus, a 0th-order diffraction light (a regularlyreflected light) is shield ed by the straight-line-shaped fine mirror240 while a first-order diffraction light and higher-order diffractionlights pass through the objective lens 201. Note that it is desirable todesign the straight-line-shaped fine mirror 240 into a band of asufficiently fine straight-line shape so that, on the surface of thespatial filter 202, the functions of the spatial filter 202 can beexecuted.

[0306] Next, connection of the defect inspecting apparatus provided bythe present invention to external equipment is explained. As describedabove, the CPU 471 controls the entire defect inspecting apparatusprovided by the present invention. For this reason, data such as resultsof inspection and conditions for inspection such as particularly athreshold-value map is stored in the storage unit 427 connected to theCPU 417. It is also desirable to communicate the results of inspectionand conditions for inspection stored in the storage unit 427 to anothercomputer through a local area network 428 or a modem. In particular, byconnecting the defect inspecting apparatus to the Internet, informationsuch as improvements of the conditions for inspection and states ofproblems encountered in the defect inspecting apparatus can be exchangedbetween the user utilizing the defect inspecting apparatus and themanufacturer of the apparatus. If information exchanged between the userand the manufacturer of the defect inspecting apparatus is encrypted byusing an encryption key known by both the user and the manufacturer,security of data can be protected. In addition, information such asimprovements of the conditions for processing and states of problemsencountered in the processing apparatus based on results of inspectionof substrate for a defect such as a foreign particle produced by thedefect inspecting apparatus can also be exchanged between the userutilizing the processing apparatus and the manufacturer of theapparatus.

[0307] Further, by designing the image-signal processing unit 400 as aprogrammable system, algorithms adopted by the units 400 shown in FIGS.4, 28, 29, 30 and 31 can each be implemented as a program which can beexecuted by the system. These algorithms each keep up with partialfluctuations in signal intensity caused by interference of typically anoxide film on the surface of a wafer. It is thus possible to implementan algorithm for dealing with the so-called color irregularities.

[0308] The following description explains lines and methods using thedefect inspecting apparatus provided by the present invention asdescribed so far to fabricate semiconductors by referring to FIGS. 32 to34.

[0309] As shown in FIG. 32, a line using the defect inspecting apparatusprovided by the present invention to fabricate semiconductors comprisesfabrication processes 601 to 609, defect inspecting apparatuses 610 to613, a probe inspection process 614 and a data analyzing system 613.

[0310] Having a big effect on or greatly affecting the yield, thefabrication processes 601, 605, 608 and 609 are monitored all the timeby the defect inspecting apparatus 612 such as the one provided by thepresent invention. If an abnormality is detected between the fabricationprocesses 601 and 606 by this monitoring, the fabrication processes 602,603 and 604 are monitored by the defect inspecting apparatus 610 todetermine the abnormality or to identify the failing piece of equipment.The particularly important fabrication process 607 is monitoreddedicatedly by the defect inspecting apparatus 611.

[0311] By the way, in order to allow only a desired process to beinspected for a foreign particle or an outermost surface in the desiredprocess to be inspected for a defect such as a foreign particle attachedthereto with a high degree of precision, an inspection for a defect suchas a foreign particle is implemented by using the defect inspectingapparatus 612 provided by the present invention before and after thedesired process and, then, a result of the pre-process defect inspectionis compared with a result of the post-process defect inspection to finda logical difference. In a judgment on the existence of a defect such asa foreign particle based on the logical difference, a foreign particlegenerated before the process must not be incorrectly interpreted as adefect introduced during the process. A pre-process defect should ratherbe ignored. This is because a pre-process defect leads to a measure toprevent a defect based on a wrong judgment.

[0312] By merely using the logical difference described above, however,it is not always possible to detect only a defect such as a foreignparticle generated in the process in question due to the followingreasons.

[0313] For example, a film is created in a film formation process on asurface having a defect such a foreign particle. Thus, the size of thedefect such as a foreign particle increases, raising the inspectionsensitivity. As a result, a defect that has been existing since a timeprior to the film formation process is detected after the process. Thatis to say, the defect that has been existing since a time prior to thefilm formation process was not detected before the process but is foundafter the process and is incorrectly regarded as a defect generatedduring the process.

[0314] In order to solve this problem, in an inspection prior to thefilm formation process, the multiplier ml is typically reduced todecrease a threshold value and to increase the inspection sensitivity.In this way, a defect that has been existing since a time prior to thefilm formation process can be detected and an incorrect judgment can beavoided. If the inspection sensitivity prior to the film formationprocess is increased as described above, however, the number ofincorrect detection cases each generating false information alsoincreases. By computing a logical difference (B-A) between resultsobtained before and after a process as shown in FIG. 51, nevertheless,this problem can be solved.

[0315] However, conditions of a surface before and after a process mayvary from area to area in a chip of the inspected substrate 1. For thisreason, even if threshold values are decreased entirely before theprocess, the background level increases. As a result, the thresholdvalues increase and there is introduced an area which is in fact in anuninspectable state or a low-sensitivity state. An infinitesimal defectexisting in an area in such a state can not be detected.

[0316] In order to solve the problem described above, the CPU 417 of thecentral processing unit 400 of the defect inspecting apparatus 612judges a defect to have been generated in a process P only if, forIb<Tb, Ia>Tha is detected and Ia>κ×Thb. That is to say, a defect isjudged to have been generated during a process P only when no defect isdetected in an inspection prior to the process P even at a highestpossible inspection sensitivity but the defect is detected in aninspection after the process P even if the inspection sensitivity isreduced and the threshold value is increased. If no defect is detectedin an inspection after the process P when the inspection sensitivity isreduced and the threshold value is increased by κ times, processing toignore defects is carried out to avoid an incorrect judgment, becausethe possibility in which a defect is judged to have been generatedduring the process P is reduced. Of course, if Ib≦Thb, the CPU can judgea defect to have been generated before the process P.

[0317] The symbol Ia denotes the level of a detection signal of a defectdetected in an inspection after the process P and the symbol Ib denotesthe level of a detection signal of a defect detected in an inspectionprior to the process P. The symbol Tha denotes the level of a thresholdvalue obtained from the threshold-value-map storage means 419 after theprocess P and the symbol Thb denotes the level of a threshold valueobtained from the threshold-value-map storage means 419 prior to theprocess P at a lowest possible inspection. The symbol κ denotes acoefficient which is greater than 1 and determined in accordance withThb. It should be noted that the comparison circuit 414 employed in theimage-signal processing unit 400 of the defect inspecting apparatuscompares Ia with Tha and Ib with Thb.

[0318] Thus, the aforementioned processing to form a judgment on theexistence of a defect such as a foreign particle carried out by the CPU417 needs threshold-value levels (a threshold-value image) of all chipareas or conforming areas prior to the process (in some cases, after theprocess) which have been obtained from the threshold-value-map storagemeans 419 and stored in the storage unit 427. The CPU 417 also needsdefect-detection signals before and after the process which have alsobeen obtained from the memory 404 and stored in the storage unit 427.What is important here is the fact that information of a threshold-valuemap for inspections before a process is stored in the storage unit 427in advance and that the coefficient κ is determined to be used indetermination of a threshold value (κ×Tha) for an inspection after theprocess by using the information of the threshold-value map. As a matterof course, Tha is computed by the threshold-value computing means 418 inan inspection after the process.

[0319] The following description explains monitoring techniques adoptedby the defect inspecting apparatus 612 to monitor the fabricationprocesses 602, 603 and 604. According to a first monitoring technique,attention is paid to a particular wafer in a lot and the wafer ismonitored for changes in state of attachment of a defect such as aforeign particle to the wafer every time the wafer goes through each orthe processes. According to a second monitoring technique, attention ispaid to a particular piece of fabrication equipment or a particularfabrication process and, by monitoring the states of a wafer before andafter the particular process, the state of the particular piece offabrication equipment or the particular fabrication process can bemonitored. A point common to the two monitoring techniques is that thestate of a fabrication process is monitored. However, it is an object ofthe first monitoring technique to compare fabrication processes witheach other, while it is an object of the second fabrication technique tocompare changes of a fabrication process with time with each other. Thatis to say, it is an object of the second fabrication technique tomonitor an accident such as a sudden generation of a foreign particle orto evaluate an effect obtained as a result of implementation of somemeasures to reduce the number of defects such as foreign particles.

[0320] The defect inspecting apparatus 612, in particular, control topay attention to a specific fabrication process or a specific piece offabrication equipment for the process, allows the user to know how thenumber of defects generated in the process can be increased or reduced.In addition, from the size of a detected foreign particle, the controlparticularly determines the fatality of the inspected wafer caused bythe foreign particle in the fabrication process, hence, allowing theimportance of a measure taken for the foreign particle and a motive forimplementation of the measure to be known. The control is thus veryeffective. That is to say, by knowing the scale of an effect of ameasure taken for a defect such as a foreign particle, the user becomesmore strongly conscious of awareness of the measure, being led to anaction taken to implement the measure.

[0321] As described above, data obtained from the monitoring is suppliedto the data analyzing system 613 for analyzing, among other things,generation of an abnormality, its correlation with data received fromthe probe inspection process 614 and its correlation with the yield.

[0322] In addition, as the defect inspecting apparatuses 610, 611 and612 described above, defect inspecting apparatuses adopting opticalbright visual-field inspection and SEM inspection techniques can beemployed besides the defect inspecting apparatus provided by the presentinvention. These defect inspecting apparatuses have their owncharacteristics so that foreign particles that can be detected by theseapparatuses are different from each other. Thus, by combining thesedefect inspecting apparatuses, the total reliability of the defectinspection can be increased. In addition, these defect inspectingapparatuses have different inspection times or inspection throughputsdue to differences in detection principle. While the laser scatteringtechnique adopted by a defect inspecting system for a high throughput issuitable for inspection of an inspected object for an infinitesimalparticle, the complementation rate during the inspection is low due tolaser interference. On the other hand, while the optical brightvisual-field inspection technique has a high complementation rate, itsthroughput is low due to the fact that a high resolution is required ina sampling operation for comparison inspection. In the case of aninspection technique using an electron beam, it is difficult to increasethe inspection speed since the SN ratio is low. However, this techniqueis suitable for high-resolution inspection of an object for a defectsuch as a bad electrical conduction.

[0323] In an LSI fabrication process, systemization of these defectinspecting apparatuses is required along with a need for considerationof the sensitivity, the throughput and detectable objects.

[0324] By increasing the number of defects such as foreign particlesthat can be detected by each of the defect inspecting apparatuses from adomain 24 to a domain 27, from a domain 25 to a domain 28 and from adomain 26 to a domain 29 as shown in FIG. 33, the total number ofdetection cases of the system can be raised. As a result, it is possibleto construct a system having a high performance as a whole.

[0325]FIG. 34 is a diagram showing a curve 30 representing changes inyield which are obtained during a build-up time of a mass production.The diagram also shows a curve 31 representing changes indetected-defect count. As shown in the figure, as the yield increases,the number of detected defects decreases. Even in a build-up state ofthe yield, however, the number of detected defects may increase all of asudden, decreasing the yield. In such a case, the generation of thedefects is recognized quickly and production based on fabricationprocesses causing the defects needs to be halted temporarily in order todetermine a countermeasure for causes of the generation of the defects.That is why the defect inspecting apparatus provided by the presentinvention is required.

[0326] As described above, according to the present invention, theefficiency of illumination can be increased and the intensity of adiffraction light generated by a pattern on a substrate such as an LSIpattern can be reduced by using a spatial filter and adjusting thedirection of the illumination. In addition, it is possible to decrease athreshold value at each of positions on a chip with variations differentfrom each other. As a result, there is exhibited an effect of acapability of inspecting a substrate such as an LSI wafer for a foreignparticle or a defect existing on the substrate with a high degree ofsensitivity at a high throughput.

[0327] In addition, according to the present invention, by using anordinary TDI image sensor with a high sensitivity, there is exhibited aneffect of a capability of detecting an infinitesimal foreign particleand a defect existing on an inspected substrate, on which repetitive andnon-repetitive patterns coexist with each other, with a high degree ofsensitivity at a high speed.

What is claimed is:
 1. A defect inspection method comprising: anillumination process of radiating an illumination slit-shaped beamcomprising lights substantially parallel to a longitudinal direction toa substrate serving as an object of inspection and having circuitpatterns created thereon in a direction inclined at a predeterminedgradient relative to the direction of a line normal to said substrateand inclined at a predetermined gradient on a surface with respect to agroup of main straight lines of said circuit patterns with itslongitudinal direction oriented almost perpendicularly to a direction ofa movement of a moving stage for mounting and moving said inspectedsubstrate; a detection process of receiving a scattered light reflectedby a defect such as a foreign particle existing on said inspectedsubstrate illuminated in said illumination process and converting saidreceived light into a detection signal by using an image sensor; and adefect judging process of extracting a signal indicating a defect suchas a foreign particle on the basis of said detection signal output insaid detection process.
 2. A defect inspection method according to claim1 wherein a diffraction-light pattern of at least a repetitive patternamong said circuit patterns existing on said substrate serving as anobject of inspection is shielded by using a spatial filter in saiddetection process.
 3. A defect inspection method according to claim 1wherein, in said defect judging process, a signal indicating a defectsuch as a foreign particle is extracted from said detection signal byusing a criterion set on the basis of a variation computed from saiddetection signal generated from locations at which the same circuitpatterns are naturally created or positions in close proximity to saidlocations.
 4. A defect inspection method according to claim 1 wherein,in said defect judging process, a signal indicating a defect such as aforeign particle is extracted from said detection signal on the basis ofa criterion set for each of a variety of areas constituting said circuitpattern.